Version July 2025
INTRODUCTION —
This topic will discuss general principles of systemic treatment for patients with metastatic colorectal cancer (mCRC). Specific details on the approach to initial and subsequent systemic therapy in unresectable mCRC are discussed separately.
●(See "Initial systemic therapy for metastatic colorectal cancer".)
●(See "Second- and later-line systemic therapy for metastatic colorectal cancer".)
SYSTEMIC THERAPY
Available agents — Many systemic agents are used to treat mCRC, in combination with other drugs and as monotherapy. These include chemotherapy (fluorouracil [FU], oxaliplatin, irinotecan, among others) (table 1), antiangiogenic agents, molecularly targeted agents, and immune checkpoint inhibitors. Available agents that are used as part of initial therapy and later lines of therapy for mCRC are discussed separately.
Many patients with mCRC are treated with initial combination systemic therapy, particularly those whose metastases might be potentially resectable after an initial response to chemotherapy. This approach must take into account the potential toxicities of combination therapy. Further details are discussed separately.
PREDICTIVE BIOMARKERS —
Predictive biomarkers (specific targetable molecular alterations found in colorectal cancer [CRC]) are used to select therapy for mCRC. Gene profiling of tumor tissue (ie, with next-generation sequencing) should be obtained immediately after a diagnosis of mCRC to determine the presence of these molecular alterations, which influence management.
RAS — Metastatic colorectal cancer (mCRC) tumors are either RAS wild-type or RAS mutated. The molecular genetics and frequency of RAS mutations in mCRC are discussed separately. (See "Molecular genetics of colorectal cancer", section on 'RAS'.)
Assessing the RAS status of a tumor permits the selection of individuals who might benefit from specific strategies, particularly those targeting the epidermal growth factor receptor (EGFR).
RAS testing — All patients with mCRC who are eligible for EGFR inhibitors should have tumor tissue tested for mutations in both KRAS and NRAS exons 2 (codons 12 and 13), 3 (codons 59 and 61), and 4 (codons 117 and 146). Several companion diagnostic tests are approved for extended RAS testing (KRAS exons 2,3, and 4 and NRAS exons 2, 3, and 4). These include the PRAXIS Extended RAS Panel, FoundationOne CDx, and xT CDx [1].
In patients with mCRC, tumor tissue (either from the primary tumor or metastatic sites) remains the gold standard for evaluating for activating RAS mutations. KRAS or NRAS are detected with good concordance between the primary tumor and synchronous distant metastases, but not lymph node metastases [2,3]. However, in some settings, rebiopsy of metastases for RAS mutation analysis may be warranted. In observational studies of patients with colorectal cancer that assessed RAS mutations in the primary tumor versus recurrent tumors, the rate of discordant results in RAS status was estimated at 20 percent [4].
What is the role of ctDNA? — The use of circulating tumor deoxyribonucleic acid (ctDNA) to confirm RAS mutation status in mCRC is evolving. Further data are necessary prior to the routine use of ctDNA to select treatment for mCRC, as some studies suggest discordance between the genotyping results on tissue versus ctDNA. Tumor tissue genotyping should be used to confirm the results from ctDNA testing, if obtained. For patients where access to tissue is unavailable or difficult to obtain, treatment may be based on actionable alterations identified on ctDNA analysis [5]. (See "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'Multipanel somatic (tumor) and germline genomic testing'.)
The use of ctDNA (or "liquid biopsy") obtained from the blood of patients with cancer can be used to detect and quantify tumor-specific genetic alterations, including RAS mutations. One advantage of ctDNA is the potential for reducing turnaround time on mutation results, although this is based on retrospective data with a limited number of cases [6].
Studies are also conflicting for concordance between the genotyping results of ctDNA assays and tumor specimens. In some studies, the overall concordance between tumor and plasma RAS mutational status (a summation of true positives and true negatives) is 82 to 93 percent [6-13]. However, other studies have reported lower rates of concordance (61 to 78 percent), especially in certain metastatic sites including the lung and peritoneum [6,9,14,15]. In one meta-analysis of 21 studies evaluating the effectiveness of ctDNA for detection of KRAS mutations, sensitivity and specificity were 67 and 96 percent, respectively [12].
Impact of RAS status on the use of EGFR inhibitors — For patients with mCRC whose tumors are RAS mutant, we do not use epidermal growth factor receptor (EGFR) inhibitors (cetuximab or panitumumab) either alone or in addition to chemotherapy. Tumors that harbor activating mutations in RAS (most commonly KRAS but also NRAS) are resistant to EGFR inhibitors due to constitutive activation of the RAS pathway. Clinical trials also confirm that EGFR inhibitors have limited clinical benefit or inferior survival outcomes in RAS-mutated CRC. (See "Molecular genetics of colorectal cancer", section on 'Molecular mechanism of RAS mutations'.)
Exceptions are KRAS G12C mutant tumors, which can be treated with the combination of adagrasib plus cetuximab or sotorasib plus panitumumab as subsequent therapy. (See "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS-mutated tumors'.)
Patients with mCRC and whose tumors are RAS and BRAF V600E wild-type are eligible for treatment with EGFR inhibitors (cetuximab or panitumumab). (See "Initial systemic therapy for metastatic colorectal cancer", section on 'RAS/BRAF wild-type tumors' and "Initial systemic therapy for metastatic colorectal cancer", section on 'Benefit of cetuximab and panitumumab'.)
Clinical studies in patients with RAS-mutated mCRC have demonstrated no benefit for EGFR inhibitors. Data are as follows:
●KRAS mutations in exon 2 – The most common RAS mutations in mCRC are KRAS mutations in exon 2 (codons 12 and 13). Patients with these tumors derive limited benefit from the use of EGFR inhibitor-based therapy [16-28]. In addition, some studies also demonstrated inferior progression-free survival (PFS) with this approach [18,29]. As examples:
•In a systematic review of four randomized trials [17,18], among patients with KRAS exon 2 mutant mCRC, the addition of an EGFR inhibitor to either chemotherapy (for treatment-naïve mCRC in the CRYSTAL and OPUS trials [17,18]) or best supportive care (for treatment-refractory mCRC in the C0.17 trial and in another trial [19,22]) did not confer a PFS (hazard ratio [HR] 1) or overall survival (OS; HR 1) advantage [27]. Further details on these individual trials are discussed separately. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'Benefit of cetuximab and panitumumab' and "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'No prior initial therapy with cetuximab/panitumumab' and "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy", section on 'RAS/BRAF wild-type disease'.)
•A randomized phase III trial (PRIME) of patients with previously untreated mCRC included a subgroup of 440 patients with KRAS exon 2 mutations. In this subgroup, the addition of panitumumab to FOLFOX worsened PFS (median 7.3 versus 8.8 months, HR 1.29, 95% CI 1.04-1.62) and failed to improve OS (median 16 versus 19 months, HR 1.24, 95% CI 0.98-1.57) [29]. Further details on the PRIME trial are discussed separately. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'Benefit of cetuximab and panitumumab'.)
Similar results were also seen in a separate randomized phase II trial (OPUS) evaluating the addition of cetuximab to FOLFOX. In this study, among the subgroup of 99 patients with KRAS exon 2 mutated tumors, FOLFOX plus cetuximab resulted in inferior PFS relative to FOLFOX alone (median PFS 6 versus 9 months, HR 1.83, 95% CI 1.10 to 3.06) [18]. Further details on the OPUS trial are discussed separately. (See "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy", section on 'RAS/BRAF wild-type disease'.)
The KRAS G13D mutation may be an exception. Data, including several meta-analyses, are conflicting as to whether this mutation confers resistance to EGFR inhibitors or not [30-36].
For patients with KRAS G12C mutated mCRC, the KRAS G12C inhibitors adagrasib and sotarasib are used either alone in combination with EGFR inhibitors (cetuximab and panitumumab, respectively) as subsequent therapy. Further details are discussed separately. (See "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS-mutated tumors'.)
●Other RAS mutations – Similarly, tumors with lower frequency KRAS mutations outside of exon 2 and NRAS mutations also do not benefit from EGFR inhibitors [3,24,37-43]. As examples,
•In a meta-analysis of nine randomized trials that evaluated EGFR inhibitor-based therapy in mCRC, no difference in PFS or OS benefit was demonstrated between tumors with RAS mutations other than exon 2 (KRAS exon 3 and 4 and NRAS exons 2, 3, and 4) and tumors with KRAS exon 2 mutations [43].
•In a subgroup analysis of the PRIME trial by mutational status, relative to the absence of a RAS mutation, RAS mutations other than KRAS exon 2 were a negative effect modifier for the addition of panitumumab to FOLFOX on both OS and PFS [37]. These data suggest that RAS mutations outside of exon 2 are also negative predictive factors for survival.
BRAF mutations — For patients with mCRC that are BRAF V600E mutated and RAS wild-type, we do not use EGFR inhibitors (cetuximab or panitumumab) as single agents in this population. This mutation induces resistance to EGFR inhibitors, and randomized trials conducted in this population suggest limited benefits.
Of note, cetuximab can be combined with encorafenib, a BRAF inhibitor, to overcome tumor resistance to EGFR inhibitors, both as initial and subsequent therapy. Further details are discussed separately. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'RAS wild-type, BRAF V600E-mutant tumors' and "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS wild-type, BRAF mutated tumors'.)
BRAF is a component of the RAS-RAF-MAPK signaling pathway. Activating BRAF mutations, which are mutually exclusive with KRAS mutations, are found in approximately 5 to 12 percent of mCRCs. BRAF mutations (most of which are V600E mutations) have consistently been associated with poor prognosis in mCRC [44-50]. (See "Pathology and prognostic determinants of colorectal cancer", section on 'RAS (KRAS, NRAS), BRAF, and EGFR'.)
●V600E mutations – Studies demonstrate that a response to EGFR inhibitors (either alone or in combination with chemotherapy) is unlikely in patients whose tumors harbor BRAF V600E mutations, even if they are RAS wild-type [51-53]:
•One analysis of 10 randomized trials comparing cetuximab or panitumumab alone or plus chemotherapy with standard therapy or best supportive care included one phase II and nine phase III trials; six were conducted in the first-line treatment setting, two for second-line therapy, and two in patients with chemorefractory disease [51]. Among patients with RAS wild-type/BRAF V600E mutant tumors, compared with control regimens, the addition of an anti-EGFR monoclonal antibody did not significantly improve PFS (HR 0.88, 95% CI 0.67-1.14), OS (HR 0.91, 95% CI 0.62-1.34), or objective response rate.
•A similar conclusion was reached in an individual patient data analysis derived from the ARCAD database of 10 randomized trials of first-line targeted therapies [53].
•Another analysis included eight randomized trials, four conducted in the first-line setting, three in the second-line setting, and one in patients with chemorefractory disease [52]. Among patients with RAS wild-type/BRAF V600E mutant mCRC, there was no significant OS benefit for the addition of an anti-EGFR monoclonal antibodies (HR 0.97, 95% CI 0.67-1.41). By contrast, OS was significantly greater in patients with RAS wild-type BRAF wild-type tumors (HR 0.81, 95% CI 0.7-0.95). When comparing the OS benefit between BRAF V600E mutant and BRAF wild-type tumors, the test for interaction was not statistically significant, leading the authors to conclude that the observed differences in the effect of anti-EGFR monoclonal antibodies on OS according to BRAF V600E mutation status could have been due to chance, and that the evidence was insufficient to state that mutant tumors attain a different treatment benefit from anti-EGFR agents compared with individuals with BRAF wild-type tumors.
•In a phase II trial (FIRE-4.5; AIO KRK0016), 109 patients with previously untreated RAS wild-type BRAF V600E-mutated mCRC were randomly assigned to oxaliplatin plus irinotecan, leucovorin (LV), and short-term infusional fluorouracil (FU; FOLFOXIRI) plus either bevacizumab or cetuximab [54]. Compared with FOLFOXIRI plus bevacizumab, FOLFOXIRI plus cetuximab decreased the objective response rate (51 versus 67 percent) and PFS (median 7 versus 11 months, HR 1.89). There was a nonstatistically significant trend towards inferior OS for FOLFOXIRI plus cetuximab (median 13 versus 17 months).
●Other BRAF mutations – Less is known about BRAF mutations outside of codon 600, which account for approximately one-fifth of all BRAF mutations in mCRC [55]. From a prognostic standpoint, patients with mCRC whose tumors harbor a non-V600 mutation seem to have a better median OSl than do those with either a V600E mutation or a BRAF wild-type tumor (61 versus 11 versus 43 months, respectively) [55]. However, there are very few data addressing the predictive value of non-V600 BRAF mutations for response to anti-EGFR agents [56-58], and this remains an area of active investigation. (See "Pathology and prognostic determinants of colorectal cancer", section on 'RAS (KRAS, NRAS), BRAF, and EGFR'.)
dMMR/MSI-H tumors — Approximately 3.5 to 6.5 percent of patients with mCRC have deficiency in mismatch repair (dMMR) enzymes, the biologic footprint of which is microsatellite instability high (MSI-H). Cancers with dMMR/MSI-H are uniquely susceptible to immune checkpoint inhibitors, and this is a reasonable first-line approach for appropriately selected patients. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'DNA mismatch repair deficient/microsatellite unstable tumors' and "Overview of advanced unresectable and metastatic solid tumors with DNA mismatch repair deficiency or high tumor mutational burden", section on 'Biologic principles'.)
TMB-H tumors — High tumor mutational burden (TMB-H) can be found in a variety of tumors, including colorectal cancer. Such tumors may be responsive to immune checkpoint inhibitors. Further details are discussed separately. (See "Overview of advanced unresectable and metastatic solid tumors with DNA mismatch repair deficiency or high tumor mutational burden", section on 'Tumors with high mutational burden'.)
POLE and POLD1 mutated tumors — Mutations in the polymerase epsilon (POLE) and polymerase delta1 (POLD1) genes can result in tumors with DNA proofreading deficiencies and a TMB-H, or high number of somatic mutations. POLE and POLD1 mutated tumors typically contain over 100 mutations per megabase [mut/Mb] [59]. POLE mutations occur more frequently in mismatch repair proficient (pMMR) tumors, while POLD1 mutations occur more frequently in dMMR/MSI tumors [60]. (See "Overview of advanced unresectable and metastatic solid tumors with DNA mismatch repair deficiency or high tumor mutational burden".)
Among patients with CRC, the frequency of POLE and POLD1 mutations is approximately 2 to 4 percent for all stages and less than 1 percent for those with mCRC [60,61]. Patients with CRC whose tumors contain a POLE or POLD1 mutation are more likely to be male, of younger age, have a right-sided primary tumor, and also have less common KRAS mutations (such as A146T) [60,62]. Data also suggest that in mCRC, POLE and POLD1 mutations are associated with increased clinical responses to immune checkpoint inhibitors [60,63-65].
HER2-positive tumors — Approximately 3 to 5 percent of CRCs have amplification of the human epidermal growth factor receptor 2 (HER2) oncogene or overexpress its protein product, HER2. HER2-targeted therapies are used to treat patients with HER2-overexpressing mCRC who progress on initial chemotherapy. Further details on available agents are discussed separately. (See "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS wild-type, HER2 overexpressors'.)
TRK-fusion-positive tumors — Tumors that harbor molecular alterations in the neurotrophic tyrosine receptor kinase (NTRK) gene produce tropomyosin receptor kinase (TRK) fusion oncoproteins. Such tumors can be treated with agents that target these TRK fusion oncoproteins, such as larotrectinib or entrectinib. Further details are discussed separately. (See "TRK fusion-positive cancers and TRK inhibitor therapy".)
Other biomarkers — EGFR amplification is not an established predictive biomarker for mCRC. Some [66-68], but not all studies [20,69-71], suggest an association between EGFR copy number and response to EGFR inhibitors. However, the clinical use of EGFR amplification to select patients for therapy is limited by the lack of standardization of fluorescence in situ hybridization technology and scoring [67,70].
TREATMENT GOALS —
The goals of chemotherapy for mCRC differ according to the clinical scenario. For most patients, treatment will be palliative and not curative (a fact that may not be understood by patients [72]), and the treatment goals are to prolong overall survival (OS) and maintain quality of life (QOL) for as long as possible.
Potentially resectable disease — However, some patients with metastatic disease (particularly those with liver-limited metastases) can be surgically cured of their disease. Even selected patients with initially unresectable liver metastases may become eligible for resection if the response to chemotherapy is sufficient.
This approach has been termed "conversion therapy" [73] to distinguish it from "neoadjuvant therapy," which applies to preoperative chemotherapy given to patients who present upfront with apparently resectable disease. The key parameter for selecting the specific regimen in this scenario is not survival or improved QOL, but instead, response rate (ie, the ability of the regimen to shrink metastases) [74]. (See "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy", section on 'Patients with initially unresectable metastases'.)
Nonresectable disease — The following general principles guide the use of palliative chemotherapy in the setting of nonoperable disease:
●In general, for patients without symptomatic disease (ie, the majority of patients), delaying tumor progression for as long as possible is just as important as induction of a tumor response. In the palliative setting, objective response rate is not the best indicator of treatment benefit (prolonged OS and/or progression-free survival [PFS]) [75-77]. Thus, achieving stable disease as the best response to therapy might be designated as a treatment success. (See 'Assessing treatment response' below.)
●The model of distinct "lines" of chemotherapy (in which regimens containing non-cross-resistant drugs are each used in succession until disease progression) is being abandoned in incurable metastatic mCRC in favor of a "continuum of care" approach [78]. This implies an individualized treatment strategy that may include phases of maintenance chemotherapy interspersed with more aggressive treatment protocols, as well as reutilization of previously administered chemotherapy agents in combination with other active drugs.
The following sections will emphasize the practical issues that arise when choosing the appropriate treatment strategy for individual patients with inoperable mCRC. Specific recommendations for therapy as well as management of patients with potentially resectable liver metastases are discussed separately. (See "Initial systemic therapy for metastatic colorectal cancer" and "Second- and later-line systemic therapy for metastatic colorectal cancer" and "Management of metastatic colorectal cancer in older adults and those with a poor performance status" and "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy".)
SYSTEMIC THERAPY VERSUS SUPPORTIVE CARE —
Systemic fluorouracil (FU)-based chemotherapy produces meaningful improvements in median survival and progression-free survival (PFS) compared with best supportive care (BSC) alone [79-81]. These benefits are most pronounced with regimens containing irinotecan or oxaliplatin in combination with FU. Although no trial has compared these regimens with BSC alone, median survival durations in clinical trials of oxaliplatin- and irinotecan-containing chemotherapy now consistently exceed two years; by contrast, for patients with unresectable mCRC who receive BSC alone, median survival is approximately five to six months [79-81].
Long-term survival is improving over time with the availability of more active anticancer agents [82-85]. As an example, in a report of pooled data from North Center Cancer Treatment Group trials conducted in the FU plus leucovorin (LV) era, only 1.1 percent of patients were alive at five years [86]. By contrast, in a report from the phase III FIRE-3 trial (first-line irinotecan with short-term infusional FU plus LV [FOLFIRI] plus either bevacizumab or cetuximab), the five-year survival rate for patients with RAS wild-type tumors treated with FOLFIRI plus cetuximab was approximately 20 percent [87]. Although many of the survival gains are attributable to advances in chemotherapy treatment, more aggressive use of surgical resection of metastatic disease has also contributed [84]. (See "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy" and "Surgical resection of pulmonary metastases: Outcomes by histology", section on 'Colorectal cancer'.)
TIMING OF SYSTEMIC THERAPY —
Although the value of early chemotherapy versus treatment deferral until symptoms develop is controversial, we suggest instituting chemotherapy at diagnosis for patients with categorically unresectable mCRC, and when possible, before patients become symptomatic.
Many patients with mCRC are asymptomatic. Data are limited on optimal timing of chemotherapy, and the only randomized trials directly addressing this issue studied regimens like fluorouracil (FU) and leucovorin (LV):
●In an early trial in which 182 patients with asymptomatic mCRC were randomly assigned to initial or deferred chemotherapy with sequential methotrexate, FU, and LV, earlier treatment was associated with improvements in median survival (14 versus 9 months), symptom-free interval, and progression-free survival (PFS) [79].
●In a combined analysis of 168 asymptomatic patients who were enrolled in two trials randomly testing early versus delayed FU-based chemotherapy, there was a non-statistically significant two-month benefit in median survival with early treatment (13 versus 11 months) [88].
Whether these results can be extrapolated to patients treated with irinotecan, oxaliplatin, or biologic therapies, especially in the era of modern diagnostic procedures that can detect lower-volume metastatic disease, is unclear. Regimens such as these are associated with clear-cut survival benefits. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'Initial doublet combinations versus sequential single agents'.)
Data suggest patients with a low burden of disease can be followed closely, and that such an initial period of observation does not compromise life expectancy. As an example, in a retrospective study of 736 patients with mCRC, 377 patients (51 percent) received immediate chemotherapy, 167 patients (23 percent) did not receive chemotherapy because they were deemed inappropriate for therapy or refused, and 192 patients (26 percent) adopted a "watch and wait" policy initially, 168 of whom eventually received chemotherapy (at a median of 3.7 months from diagnosis) [89]. Patients who adopted a "watch and wait" policy were asymptomatic with low bulk of metastatic disease. Compared with immediate treatment, the fraction of patients in the delayed chemotherapy group who eventually received treatment with all active agents was slightly less (30 versus 39 percent), but the median overall survival (OS) was superior (27 versus 17 months). Importantly, these data are not from a randomized trial, and the longer survival in the "watch and wait group" is most likely due to selection bias (ie, choosing a group of patients with more favorable disease biology for deferred treatment).
CHEMOTHERAPY DOSING IN OBESE PATIENTS —
For cancer patients with a large body surface area (BSA), chemotherapy drug doses are often reduced because of concern for excess toxicity. However, there is no evidence that fully dosed obese patients experience greater toxicity from chemotherapy for mCRC; furthermore, obese patients who are given reduced doses may have inferior outcomes [90]. Although limited, the available data do not support the policy of routine dose reduction (or capping the maximal BSA to 2 m2) for obese patients with mCRC. Guidelines from the American Society of Clinical Oncology recommend that full weight-based cytotoxic chemotherapy doses be used to treat obese patients with cancer [91]. (See "Dosing of anticancer agents in adults", section on 'Dosing for patients with obesity and who are overweight'.)
CONTINUOUS VERSUS INTERMITTENT THERAPY —
The optimal duration of initial chemotherapy for unresectable mCRC is controversial. The decision to permit treatment breaks for responding patients must be individualized and based upon the regimen being used, tolerance of and response to chemotherapy, disease bulk and location, symptomatology, and patient preference. For many patients with chemotherapy responsive disease who do not have bulky or severely symptomatic disease, intermittent rather than continuous therapy may mitigate treatment-related toxicity, and does not appear to adversely impact overall survival (OS).
Rationale for intermittent therapy — When fluorouracil (FU) was the only treatment alternative, patients generally stayed on treatment until their disease progressed or they developed unacceptable toxicity. This typically meant that patients were treated for four to six months (the median progression-free survival [PFS] duration) and then were placed on supportive care alone until they died (median duration of survival approximately one year).
Compared with FU alone, contemporary combination chemotherapies are more effective (median survival durations now consistently approach two years), but they are also more toxic. This is particularly true for oxaliplatin-containing regimens, which cause dose-limiting cumulative neurotoxicity after three to six months; several studies have shown that more patients come off of therapy because of toxic effects than because of progressive disease [92,93]. Intermittent rather than continuous chemotherapy has the potential to improve outcomes and reduce toxicity as well as cost.
However, intermittent therapy may be appropriate for some patients and not others:
●There are many patients with small volume but multiple sites of disease who respond well to chemotherapy or have a prolonged period of disease stability. Even if their disease triples in volume off therapy, they will not likely be symptomatic or develop organ dysfunction. Patients with favorable characteristics may be able to tolerate chemotherapy-free (or at least oxaliplatin-free) intervals of multiple months per year and go on to respond favorably to drugs for many years.
●On the other end of the spectrum are patients with retained primary tumors, bulky disease, poor performance scores due to tumor related symptoms, peritoneal disease that may lead to unsalvageable bowel obstruction as the first sign of progression, and those with extensive symptomatic disease who progress through treatment regimens in quick succession with either short-lived responses or no response. These patients may be better approached with continuous chemotherapy. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'Duration of initial chemotherapy'.)
Whether continued chemotherapy provides better outcomes than intermittent therapy to best response followed by a chemotherapy "holiday" has been addressed in several trials, most of which have studied chemotherapy regimens that contain oxaliplatin, a drug that is associated with dose-limiting neurotoxicity. Intermittent oxaliplatin-free therapy can be achieved through a complete break in therapy or the use of a non-oxaliplatin-containing "maintenance regimen." (See "Overview of neurologic complications of platinum-based chemotherapy", section on 'Cumulative sensory neuropathy' and "Initial systemic therapy for metastatic colorectal cancer", section on 'FOLFOX versus FOLFIRI'.)
Patients receiving oxaliplatin — Oxaliplatin-based regimens (eg, FOLFOX [oxaliplatin plus leucovorin (LV) and short-term infusional FU]) (table 2) are commonly used for first-line chemotherapy in mCRC [94]. However, oxaliplatin is associated with a cumulative sensory neuropathy, which may be dose limiting.
Whether long-term neurotoxicity can by mitigated by intermittent oxaliplatin-free intervals has been addressed in several trials. The following represents an overview of the most important findings.
Maintenance fluoropyrimidines only
●OPTIMOX-1 – The OPTIMOX1 trial randomly assigned 620 previously untreated patients to FOLFOX, administered every two weeks until disease progression (arm A), or FOLFOX for six cycles only, followed by reintroduction of oxaliplatin at the time of progression after 12 cycles of a non-oxaliplatin-containing maintenance regimen (LV-modulated FU) [95]. The duration of disease control and OS between the continuous (arm A) and maintenance (arm B) approaches were very similar (9 versus 8.7 months, and 19.3 versus 21.2 months, respectively). Individuals in arm B had a significantly lower risk of developing grade 3 or 4 toxicity during cycles 6 to 18 (but not overall) [96].
●OPTIMOX-2 – The subsequent OPTIMOX-2 trial was initially designed as a 600 patient phase III trial, but when bevacizumab became available, accrual was halted with 202 patients enrolled [97]. OPTIMOX-2 compared six cycles of modified FOLFOX7 followed by maintenance with FU/LV (arm A) to six cycles of modified FOLFOX7 followed by a complete stop in chemotherapy (arm B). The primary endpoint was the duration of disease control, calculated as the sum of the duration of PFS both following the initial three-month course of modified FOLFOX7 (mFOLFOX7), as well as after the subsequent reintroduction of oxaliplatin. An important characteristic of OPTIMOX-2 was that randomization occurred after six cycles of therapy regardless of response, and metastases were allowed to progress back to baseline levels before FOLFOX was reintroduced.
Complete discontinuation of therapy seemed to have an adverse impact on prognosis; the group receiving maintenance therapy had significantly longer median duration of disease control and median PFS from the time of randomization; there was also a nonstatistically significant trend toward improved median OS (24 versus 20 months). These data mandate caution and both careful patient selection and vigilant patient monitoring so that therapy can be reinstated promptly at progression during chemotherapy-free intervals.
●Another multicenter trial, the CONcePT trial, in which patients were randomly assigned to continuous versus intermittent oxaliplatin (alternating every eight cycles with and without oxaliplatin) also confirmed the benefit of intermittent rather than continuous oxaliplatin for increasing time on first-line therapy for oxaliplatin/bevacizumab-based combinations [98]. Rates of peripheral sensory neuropathy were significantly lower in the intermittent therapy group.
Maintenance bevacizumab — Several trials have explored the benefit of maintenance bevacizumab in patients initially treated with a bevacizumab-containing regimen, both alone and in combination with a fluoropyrimidine.
●Bevacizumab plus a fluoropyrimidine
•CAIRO3 – The utility of maintenance treatment with capecitabine plus bevacizumab was addressed in the Dutch CAIRO3 trial, which randomly assigned 558 patients with stable disease or better after six cycles of XELOX plus bevacizumab who were not eligible for potentially curative metastasectomy to continued capecitabine (625 mg/m2 twice daily every day) plus bevacizumab (7.5 mg/kg every three weeks) or observation alone [99]. Upon first progression (PFS1), patients in both arms were supposed to be treated with XELOX plus bevacizumab until the second progression (PFS2) per protocol. The primary endpoint was PFS2, which was calculated from the time of randomization. Maintenance therapy was associated with a significantly longer PFS2 (11.7 versus 8.5 months, hazard ratio [HR] 0.67), and there was a nonstatistically significant trend toward improved OS, as well (median 21.6 versus 18.1 months, HR 0.89).
•German AIO KRK 0207 trial – Similarly, a benefit for continued fluoropyrimidine plus bevacizumab as compared with observation alone was also shown in the German AIO KRK 0207 trial, in which patients without progressive disease after six months of oxaliplatin plus a fluoropyrimidine and bevacizumab were randomly assigned to maintenance with the same fluoropyrimidine plus bevacizumab, bevacizumab alone, or observation only [100]. The primary endpoint was the "time to failure of strategy" or TFS, which included the duration of maintenance plus the time from reinduction after first progression to a second disease progression. The trial was powered to demonstrate noninferiority with a noninferiority margin set at 3.5 months, corresponding to an HR of 1.42. The median TFS in the fluoropyrimidine plus bevacizumab and observations arms was not significantly different (6.9 and 6.4 months, respectively; HR 1.26, 95% CI 0.99-1.60). However, the observation arm was not noninferior to fluoropyrimidine plus bevacizumab because the upper limit of the 95 percent confidence interval exceeded the threshold set for noninferiority (1.43). Notably, few patients in either arm were exposed to reinduction treatment (19 percent with combined therapy, and 46 percent of those undergoing observation), rendering the primary endpoint, TFS, noninformative and clinically irrelevant.
•STOP and GO trial – A slightly different approach was tested in the Turkish STOP and GO trial, in which, following six cycles of bevacizumab plus XELOX, 123 patients were randomly assigned to continued therapy or discontinuation of oxaliplatin and maintenance with bevacizumab plus capecitabine until progression [101]. The median PFS was significantly better in the group receiving maintenance therapy with bevacizumab plus capecitabine (11 versus 8.3 months), with less grade 3 or 4 diarrhea (3.3 versus 11.3 percent), hand-foot syndrome (1.6 versus 3.2 percent), and neuropathy (1.6 versus 8.1 percent).
●Bevacizumab monotherapy – For patients who have no disease progression after an initial course of bevacizumab plus oxaliplatin-containing chemotherapy, we do not offer bevacizumab alone for maintenance therapy.
The role of maintenance bevacizumab alone has been studied in three trials, all of which used different comparator arms, and all of which came to different conclusions:
•MACRO – In the Spanish MACRO trial, patients received six cycles of first-line XELOX plus bevacizumab followed by a randomization to continued therapy or bevacizumab maintenance therapy alone until progression or treatment intolerance [102]. There was no arm in which patients received no maintenance therapy. The median PFS and OS durations in patients treated with maintenance bevacizumab alone were not significantly worse, and rates of severe neurotoxicity, hand-foot syndrome, and fatigue were significantly lower. However, the trial failed to achieve its primary endpoint of noninferiority for PFS, because the projected upper limit of the 95 percent confidence interval for PFS exceeded the preset limit.
•SAKK 41-06 – In the Swiss SAKK 41-06 trial, 262 patients with mCRC were randomly assigned to bevacizumab continuation versus no maintenance after four to six months of first-line bevacizumab-containing chemotherapy (62 percent oxaliplatin-containing, 31 percent irinotecan-containing, and the rest fluoropyrimidine alone) [103]. Like the MACRO trial, the trial failed to achieve its primary endpoint of noninferiority for time to progression (TTP) with the projected upper limit of the 95 percent confidence interval for TTP exceeding the preset limit. The median TTP was 4.1 for bevacizumab continuation versus 2.9 months for no continuation (HR 0.74, 95% CI 0.57-0.95). However, in our view, this study has significant limitations; it includes trials conducted over almost two decades, contains a very heterogenous patient population, and it is heavily influenced by the COIN trial due to its size. As a result, it should not be used to justify use of bevacizumab alone as effective maintenance therapy.
•German AIO KRK 0207 trial – On the other hand, noninferiority of bevacizumab alone compared with bevacizumab plus a fluoropyrimidine was shown in the German AIO KRK 0207 trial [100]. The primary endpoint (the median TFS) in the fluoropyrimidine plus bevacizumab and bevacizumab alone arms was 6.9 and 6.1 months, respectively. Compared with fluoropyrimidine plus bevacizumab, the bevacizumab only arm was noninferior (HR 1.08, 95% CI 0.85-1.37). However, the upper boundary of the noninferiority margin was very generous (HR 1.43). Notably, few patients in either arm were exposed to reinduction treatment (19 percent with combined therapy, and 43 percent of those receiving bevacizumab alone), rendering the primary endpoint, TFS, noninformative and clinically irrelevant.
Patients initially treated with an EGFR inhibitor — For patients initially treated with an agent targeting the epidermal growth factor receptor (EGFR), we suggest maintenance therapy using FU plus the anti-EGFR agent rather than an anti-EGFR agent or fluoropyrimidine alone.
Benefit from anti-EGFR therapies is limited to patients whose tumors lack mutations in one of the RAS oncogenes (ie, wild-type RAS). (See 'RAS' above.)
Three trials have addressed the benefit of maintenance therapy with an EGFR inhibitor after initial treatment with FOLFOX plus an EGFR inhibitor:
●MACRO – The phase II MACRO-2 trial randomly assigned 193 patients with KRAS (exon 2 only) wild-type tumors to receive FOLFOX plus cetuximab for four months (eight courses) followed by either continued therapy with the same regimen or cetuximab monotherapy alone (250 mg/m2 weekly) [104]. Cetuximab monotherapy was noninferior to the combination of continued FOLFOX plus cetuximab, as judged by the primary endpoint, the proportion of patients who were progression free at nine months (60 versus 72 percent, HR 0.60, 95% CI 0.31-1.15).
●VALENTINO – On the other hand, results with panitumumab alone were inferior to maintenance treatment with FU/LV plus panitumumab following four months of induction therapy with FOLFOX plus panitumumab in the phase II noninferiority VALENTINO trial [105]. Ten-month PFS was inferior with panitumumab alone (49 versus 60 percent).
●PANAMA – A slightly different question, the benefit of adding panitumumab to LV modulated FU versus FU/LV alone after six cycles of induction therapy with FOLFOX plus panitumumab in RAS wild-type advanced CRC was addressed in the phase III PANAMA trial [106]. Median PFS, the primary endpoint, was significantly better with combined therapy as compared with LV-modulated FU alone (8.8 versus 5.7 months, HR 0.72, 95% CI 0.60-0.85), and there was also a trend to better OS that also favored maintenance panitumumab.
Patients receiving irinotecan — While intermittent treatment approaches appear to be almost mandatory for most patients receiving oxaliplatin because of cumulative neurotoxicity, there are no cumulative dose-dependent toxicities from irinotecan. For most patients who are receiving irinotecan-containing regimens, we continue treatment as long as tumor burden continues to decrease and treatment is well-tolerated. Thereafter, for patients with disease response (including those receiving concomitant therapy with an EGFR inhibitor) who desire a treatment break, intermittent therapy is an option that does not appear to compromise OS.
Intermittent therapy — In patients with mCRC who are initially treated with an irinotecan-containing regimen, studies have compared intermittent (ie, treatment-free intervals followed by reintroduction of the same systemic therapy upon disease progression) with continuous chemotherapy:
●FOLFIRI alone – One trial demonstrated that patients started on FOLFIRI (irinotecan with short-term infusional FU plus LV (table 3)) as first-line therapy had similar overall outcomes (PFS and OS) whether or not the regimen was administered continuously until progression or toxicity or in "two months on/two months off" intervals [107]. The median chemotherapy-free period in the intermittent treatment group was only three months. However, there were no demonstrable differences in treatment-related toxicity between the continuous versus intermittent treatment groups. Of note, further second- and third-line therapy did not follow a "stop-and-go" approach, so that for OS, any potential differences obtained in first-line therapy could have been obscured by subsequent treatment. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'Irinotecan-based regimens'.)
●FOLFIRI plus an EGFR inhibitor – Patients treated initially with an irinotecan plus an EGFR inhibitor may obtain similar OS benefit with less toxicity from intermittent therapy compared with continuous therapy. In a randomized phase II trial (IMPROVE), 137 patients with unresectable, previously untreated RAS/BRAF wild-type mCRC were randomly assigned to intermittent therapy with eight cycles of FOLFIRI plus panitumumab followed by a treatment-free interval and reintroduction of the same regimen at disease progression, or continuous therapy with FOLFIRI plus panitumumab until disease progression on treatment [108]. At a median follow-up of 43 months, compared with continuous therapy, intermittent therapy resulted in similar overall response rates (61 versus 68 percent), higher PFS (18 versus 11 months), and similar OS (35 versus 36 months). Intermittent therapy was better tolerated with lower rates of grade ≥3 skin toxicity (18 versus 30 percent) and fewer patients discontinued therapy for toxicity.
Maintenance therapy — For patients who are initially treated with an irinotecan-based regimen plus an EGFR inhibitor and demonstrate disease response, we do not typically use maintenance therapy with an EGFR inhibitor alone. In an open-label, noninferiority phase III trial (ERMES), 606 patients with untreated RAS/BRAF wild-type mCRC were randomly assigned to either FOLFIRI plus cetuximab for eight cycles followed by maintenance cetuximab alone or FOLFIRI plus cetuximab until disease progression [109]. At a median follow-up of 22 months, in the intention to treat population, relative to continuous FOLFIRI plus cetuximab, maintenance cetuximab failed to demonstrate noninferior PFS (median 11 versus 9 months) and demonstrated a nonstatistically significant trend towards lower OS (median 25 versus 31 months). Maintenance cetuximab was better tolerated than continuous therapy (grade 3 to 4 toxicity rate 20 versus 35 percent).
For patients initially treated with FOLFIRI plus bevacizumab and demonstrate disease response, we do not offer maintenance bevacizumab. In a randomized phase III trial (PRODIGE 9) of patients with mCRC treated with six months of induction FOLFIRI plus bevacizumab, maintenance bevacizumab failed to show an OS benefit compared with no treatment until disease progression [110].
Complete break in therapy — The data on maintenance therapy have led to the general conclusion that some form of maintenance therapy is preferred rather than a complete break in therapy in patients who are responding to or have stable disease after induction chemotherapy therapy. However, while maintenance therapy prolongs PFS compared with no maintenance therapy, none of the trials have shown that this approach is associated with better OS compared with a complete break in therapy.
Meta-analyses and clinical trials have specifically addressed the role of observation (ie, a complete break in therapy) versus maintenance treatment in patients initially treated with either oxaliplatin or irinotecan-based initial systemic therapy for mCRC, all of which have concluded that OS is not adversely impacted by a complete break in treatment:
●A network meta-analysis included 12 randomized trials comparing the different treatment strategies of continued chemotherapy, observation, and maintenance therapy (including fluoropyrimidine alone, bevacizumab alone, or fluoropyrimidine plus bevacizumab) [111]. Different induction regimens were used in the different trials, including an oxaliplatin-based regimen in nine [95,97-103,112,113], an irinotecan-based regimen in two [110,114], and mixed regimens in one trial [103].
Comparisons of any maintenance therapy versus observation demonstrated that maintenance therapy was associated with improved PFS in both direct (HR 0.63, 95% CI 0.45-0.86) and indirect analyses (HR 0.58, 95% CI 0.43-0.77), but the effect on OS was not significant (HR for the indirect analysis 0.91, 95% CI 0.83-1.01). Analyses of each specific maintenance strategy (fluoropyrimidine alone, bevacizumab alone, fluoropyrimidine plus bevacizumab) versus observation alone also found improved PFS but not OS for all comparisons.
●Similarly, an individual patient data meta-analysis of more than 4000 patients enrolled on nine trials evaluating intermittent therapy after successful completion of induction therapy (six with planned stopping of all therapy, the other three discontinuing oxaliplatin with continuation of the other regimen components as maintenance therapy) also concluded that a complete break in therapy did not adversely impact survival [115]. The overall analysis of intermittent versus continuous therapy showed no significant OS detriment from intermittent therapy (HR 1.03, 95% CI 0.93-1.14), whether from complete break (HR 1.04, 95% CI 0.87-1.26) or maintenance (HR 0.99, 95% CI 0.87-1.13). PFS results were broadly consistent with the OS results. In a preplanned analysis, thrombocytosis was confirmed as a poor prognostic factor, but it did not predict for inferior survival from a complete treatment break compared with continuous therapy (interaction HR 0.97, 95% CI 0.66-1.40).
●Additional data are available from the randomized FOCUS4-N trial, in which 254 patients with stable or responding disease after 16 weeks of induction therapy with a variety of regimens were randomly assigned to a complete break in therapy with active monitoring versus single-agent capecitabine (1250 mg/m2 twice daily on days 1 through 14 of each 21-day cycle), until progression [116]. Maintenance therapy with capecitabine doubled the TTP and return to full-dose chemotherapy (median PFS 3.88 versus 1.87 months, HR 0.40, 95% CI 0.21-0.75), but had no impact on median OS (14.8 versus 15.2 months, adjusted HR 0.93, 95% CI 0.69-1.27). Furthermore, those assigned to maintenance capecitabine had significant higher rates of cumulative toxicity, especially diarrhea, fatigue, nausea, and palmar plantar erythrodysesthesia, although these were primarily low grade.
ASSESSING TREATMENT RESPONSE —
During chemotherapy, response is typically assessed by periodic assay (every one to three months) of serum carcinoembryonic antigen (CEA) levels, if initially elevated, and interval radiographic evaluation (typically every 8 to 12 weeks, or as prompted by a rising CEA level). Although persistently rising CEA levels are highly correlated with disease progression, confirmatory radiologic confirmatory studies should be obtained prior to a change in therapeutic strategy, with the notable exception of confirmed peritoneal carcinomatosis that is not radiographically measurable.
Radiographic response — Radiographic tumor response is usually quantified using Response Evaluation Criteria In Solid Tumors (RECIST) (table 4) [117,118].
Immunotherapy using immune checkpoint inhibitors is increasingly being integrated into the care of patients with mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) mCRC. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'DNA mismatch repair deficient/microsatellite unstable tumors' and "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'dMMR/MSI-H tumors'.)
Individuals treated with immune checkpoint inhibitors for dMMR/MSI-H mCRC can have pseudoprogression [119], and objective response criteria specifically developed for these drugs should be used (eg, immune-modified RECIST [imRECIST] (table 5)). (See "Principles of cancer immunotherapy", section on 'Immunotherapy response criteria'.)
Serum tumor markers — If initially elevated, a 50 percent or greater declines in CEA from baseline to first restaging can predict disease nonprogression and correlate with favorable long-term outcomes [120]. On the other hand, persistently rising CEA levels (particularly rapidly rising levels [121]) are highly correlated with disease progression [122,123]. However, confirmatory radiologic studies are generally recommended in both settings, particularly if a change in therapeutic strategy is being evaluated because of a rising CEA. Caution should be used when interpreting a rising CEA level during the first four to six weeks of a new therapy, since spurious early elevation in serum CEA may occur, especially after oxaliplatin [124-126].
Circulating tumor DNA (ctDNA) is the fraction of circulating DNA that is derived from a patient's cancer. CRCs shed DNA into the blood, and interest in using ctDNA as a surrogate indicator of treatment response has grown as techniques to detect and quantify such DNA have improved. A meta-analysis of 24 studies on patients with mCRC reporting on the predictive or prognostic value of ctDNA concluded that a small or no early decrease in ctDNA levels during treatment was associated with short progression-free survival (PFS) and overall survival (OS), but the majority of included studies had a high risk of bias [127].
Few large prospective validation studies have been performed on ctDNA-based treatment monitoring. At least in advanced breast cancer, there are some data that suggest that ctDNA responses do not always parallel imaging-based responses [128], and no studies convincingly demonstrate improved patient outcomes or any cost savings when compared with standard of care monitoring approaches.
Thus, in our view, there is not yet enough known about the mechanisms controlling ctDNA change and how well radiologic responses or CEA changes and ctDNA markers correlate with each other to understand whether ctDNA can replace or supplement periodic assay of CEA or radiologic assessment, and the clinical utility of serial assay of ctDNA during remains uncertain. This position is consistent with a year 2018 joint review of the utility of ctDNA analysis in patients with cancer by American Society of Clinical Oncology and the College of American Pathologists, which concluded that there is insufficient evidence of clinical validity and utility for the majority of ctDNA assays in advanced cancer [129]. However, this remains an active area of research with a number of ongoing studies that should impact information on the potential future utility of ctDNA analysis in this setting.
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Colorectal cancer".)
INFORMATION FOR PATIENTS —
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Colon and rectal cancer (The Basics)")
●Beyond the Basics topics (see "Patient education: Colon and rectal cancer (Beyond the Basics)" and "Patient education: Treatment of metastatic colorectal cancer (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Available agents – Many systemic agents are used to treat metastatic colorectal cancer (mCRC), in combination with other drugs and as monotherapy. These include chemotherapy (fluorouracil [FU], oxaliplatin, irinotecan, among others), antiangiogenic agents, molecularly targeted agents, and immune checkpoint inhibitors. (See 'Systemic therapy' above.)
●Predictive biomarkers – Predictive biomarkers (specific targetable molecular alterations found in CRC) are often used to select therapy for mCRC. (See 'Predictive biomarkers' above.)
•RAS and BRAF wild-type disease – Patients with mCRC whose tumors are RAS and BRAF V600E wild-type are eligible for treatment with epidermal growth factor receptor (EGFR) inhibitors (cetuximab or panitumumab). (See "Initial systemic therapy for metastatic colorectal cancer", section on 'RAS/BRAF wild-type tumors'.)
•RAS mutant disease – RAS mutated mCRC is resistant to EGFR inhibitors (cetuximab or panitumumab). Exceptions are KRAS G12C mutant tumors, which can be treated with the combination of adagrasib plus cetuximab or sotorasib plus panitumumab as subsequent therapy. (See 'Impact of RAS status on the use of EGFR inhibitors' above and "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS-mutated tumors'.)
•BRAF V600E mutant disease – BRAF V600E mutated mCRC shows resistance to EGFR inhibitors, and we do not use them as single agents for these cancers, due to limited benefit in randomized trials. (See 'BRAF mutations' above.)
Of note, cetuximab can be combined with encorafenib, a BRAF inhibitor, to overcome tumor resistance to EGFR inhibitors, both as initial and subsequent therapy. (See "Initial systemic therapy for metastatic colorectal cancer", section on 'RAS wild-type, BRAF V600E-mutant tumors' and "Second- and later-line systemic therapy for metastatic colorectal cancer", section on 'RAS wild-type, BRAF mutated tumors'.)
•Other clinically relevant biomarkers – Other clinically relevant biomarkers include mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H), high tumor mutational burden (TMB-H), POLE and POLD1 mutations, human epidermal growth factor receptor 2 (HER2) expression, and molecular alterations in neurotrophic tyrosine receptor kinase (NTRK). (See 'dMMR/MSI-H tumors' above and 'HER2-positive tumors' above and 'TRK-fusion-positive tumors' above.)
●Treatment goals – Some patients with metastatic disease can be surgically cured of their disease, and the goal of initial chemotherapy is maximal reduction in tumor burden. For most, treatment is palliative, and the goals are to prolong overall survival (OS) and maintain quality of life (QOL) for as long as possible. (See 'Treatment goals' above.)
●Timing of therapy – For most patients, we suggest early rather than deferred initiation of chemotherapy, and when possible, before patients become symptomatic (Grade 2C). (See 'Timing of systemic therapy' above.)
●Duration of initial therapy – The optimal duration of initial chemotherapy for unresectable mCRC is controversial. The decision to permit treatment breaks for responding patients must be individualized and based upon the regimen being used, tolerance of and response to chemotherapy, disease bulk and location, symptomatology, and patient preference. For many patients with chemotherapy responsive disease who do not have bulky or severely symptomatic disease, intermittent rather than continuous therapy may mitigate treatment-related toxicity, and does not appear to adversely impact OS. (See 'Continuous versus intermittent therapy' above.)
•Patients receiving oxaliplatin – For most patients who are responding to an oxaliplatin-based initial regimen, we suggest discontinuing oxaliplatin before the onset of severe neurotoxicity (usually after three to four months of therapy) while continuing the other agents in the regimen (Grade 2C). Continuing oxaliplatin is a reasonable alternative for patients who have an ongoing response and no clinically significant neuropathy. (See 'Patients receiving oxaliplatin' above.)
A complete break in therapy is also a valid option, particularly if a complete clinical response is observed or for those with small-volume metastatic disease who have a partial response or stable disease to the initial course of chemotherapy. Decision-making should also take into account patient preference. In such cases, close follow-up with tumor assessment at two-month intervals and early resumption of chemotherapy at the first sign of progression is recommended. (See 'Complete break in therapy' above.)
•Patients receiving irinotecan – For most patients who are receiving an irinotecan-based initial regimen, we continue treatment for as long as tumor burden continue to decrease and treatment is well-tolerated. Thereafter, for patients with disease response (including those receiving concomitant therapy with an EGFR inhibitor) who desire a treatment break, intermittent therapy is an option that does not appear to compromise OS. (See 'Patients receiving irinotecan' above.)
●Response assessment – Response to chemotherapy is typically assessed by periodic assay of serum carcinoembryonic antigen (CEA) levels, if initially elevated, and interval radiographic evaluation. Although persistently rising CEA levels are highly correlated with disease progression, confirmatory radiologic confirmatory studies should be obtained prior to a change in therapeutic strategy, with the notable exception of confirmed peritoneal carcinomatosis that is not radiographically measurable. (See 'Assessing treatment response' above.)
ACKNOWLEDGMENT —
The UpToDate editorial staff acknowledges Axel Grothey, MD, who contributed to an earlier version of this topic review.
