Version July 2025
INTRODUCTION —
Dermatomyositis (DM) and polymyositis (PM) are idiopathic inflammatory myopathies characterized by proximal skeletal muscle weakness and evidence of muscle inflammation. DM, unlike PM, is characterized by the presence of various cutaneous manifestations. DM and PM may also be associated with inflammatory arthritis, interstitial lung disease, Raynaud phenomenon, and the presence of autoantibodies.
An association between inflammatory myopathy and cancer has been recognized since the report of two cases of PM and gastric cancer in 1916 [1]. The association is stronger for patients with DM than PM. The evidence for an association between cancer and inflammatory myopathy includes:
●Epidemiologic evidence from large population studies
●Close temporal relationship between the diagnosis of cancer and myopathy
●The possible improvement or resolution of myopathy after treatment of the cancer
●Relapse or development of myopathy associated with relapse of the cancer
The increased frequency of cancer in patients with inflammatory myopathy is consistent with the concept that paraneoplastic processes linked to oncogenesis and autoimmunity contribute to the disease in a subset of DM and PM cases.
Notably, the term PM is falling out of favor given the increased understanding that many cases that would previously have been classified as PM are now better classified as the antisynthetase syndrome (without a characteristic rash), overlap myositis (with another connective tissue disease), or immune-mediated necrotizing myopathy (IMNM). More commonly, patients with inclusion body myositis are incorrectly diagnosed as having PM. Occasionally, an adult-onset muscular dystrophy is misdiagnosed as PM given similar patterns of weakness and inflammation seen on muscle biopsy. While it is now understood that muscle biopsy features are distinct in IMNM, previous studies often labeled these cases as PM, assuming the primary inflammation had been missed on the muscle biopsy sampling.
Issues related to malignancy in patients with DM and PM will be reviewed here. The clinical manifestations, diagnosis, and management of both the adult and juvenile forms of these disorders are discussed separately. (See "Clinical manifestations of dermatomyositis and polymyositis in adults" and "Initial treatment of dermatomyositis and polymyositis in adults" and "Juvenile dermatomyositis and other idiopathic inflammatory myopathies: Epidemiology, pathogenesis, and clinical manifestations" and "Juvenile dermatomyositis and polymyositis: Treatment, complications, and prognosis".)’’
PATHOPHYSIOLOGY —
The precise links between malignancy and inflammatory myopathy remain incompletely understood [2,3]. However, the temporal relationship in some patients between the development of cancer and diagnosis of inflammatory myopathy is reminiscent of that seen in neurologic paraneoplastic disorders in which the antigens targeted for an immune response are expressed at high levels in both the inciting tumor and the affected neuronal tissue [4,5]. (See "Overview of paraneoplastic syndromes of the nervous system".)
Regenerating cells in myositis muscle but not in normal muscle express high levels of myositis-specific autoantigens [2]. These same antigens are expressed at high levels in several cancers known to be associated with the development of inflammatory myopathy, but not in corresponding normal tissue. These observations suggest that the link between malignancy and inflammatory myopathy relates to the expression of common autoantigens between cancer tissue and muscle tissue in some patients with dermatomyositis (DM) or polymyositis (PM), and that the immune response directed at tumor cells may also target similar autoantigens in muscle tissue resulting in muscle damage.
EPIDEMIOLOGY —
The association between malignancy and inflammatory myopathy has been supported by numerous epidemiologic studies, with the strongest association occurring in those with dermatomyositis (DM) [6-14].
Incidence — A review of 258 cases of DM and cancer reported in the literature from 1916 through the mid-1970s estimated that the incidence of cancer for patients with DM was increased five- to seven-fold compared with the general population [6]. The increased risk has subsequently been confirmed in population-based studies from a variety of countries. Standardized incidence ratios from population-based studies from Denmark [9], Australia [10], and Taiwan [11] range from approximately 3.0 to 6.0. The largest population study from Taiwan included 1,012 DM and 643 patients with polymyositis (PM) from the National Health Insurance Database from 1997-2007. Among the patients with DM, the frequency of cancer was 9.4 percent and the standardized incidence ratio (SIR) 5.11 (95% CI 5.01-5.22). In the PM group, the frequency of cancer was 4.4 percent with an SIR of 2.15 (95% CI 2.08-2.22) [11].
The cancer rates reported with PM are consistently lower than that of DM. Some investigators have questioned whether the modestly increased incidence in PM indicates a true increase in cancer risk or may reflect increased surveillance in patients with PM compared with the general population [8,13].
Types of malignancies — The types of cancer associated with inflammatory myopathy appear to mirror the incidence of cancer in the general population. As an example, a population-based study including patients from Sweden, Denmark, and Finland found an increased risk of ovarian, lung, breast, pancreatic, and colorectal cancers [15]. In another study including patients from Taiwan, nasopharyngeal carcinoma was the most common type of malignancy in patients with DM, followed by lung and breast cancer [11,16]. Ovarian, pancreatic, and gastric cancers appear to occur more frequently in patients with inflammatory myopathy than in the general population [15]. There is a strong association between ovarian cancer and the presence of the anti-transcription intermediary factor 1 (TIF1) antibody [17].
Temporal relationship — Cancer can be diagnosed before, simultaneously with, or after the diagnosis of inflammatory myopathy [11]. The peak incidence of a cancer diagnosis in DM and PM occurs simultaneously with and during the first year after the diagnosis of the muscle disease, and falls off gradually over the subsequent five years of follow-up [8,11,17-19], although there may still be some increased risk beyond five years [11,19].
In some patients, the inflammatory myopathy is diagnosed at the time of recurrence of previously diagnosed cancer. In others, previously diagnosed muscle disease becomes reactivated when the cancer appears [20,21].
RISK FACTORS —
As noted above, most studies have concluded that the risk of cancer is greater in patients with dermatomyositis (DM) than in those with polymyositis (PM). Patients with interstitial lung disease appear to have a lower frequency of malignancies [18,22,23].
Serum autoantibodies — Some serum antibodies in DM and PM confer a positive risk of malignancy, whereas others are associated with a negative risk. Consensus-based recommendations for idiopathic inflammatory myopathy (IIM)-associated cancer screening were developed by a large multidisciplinary international Expert Group with expertise in IIM and cancer screening derived from members of the International Myositis Assessment and Clinical Studies Group (IMACS). These evidence-based guidelines suggest a variable risk for malignancy depending on the associated autoantibody [24].
●High risk – Cancer-associated myositis (CAM) in adults has been associated in several studies with antibodies to transcription intermediary factor (TIF)-1gamma (also noted as anti-p155, anti-p155/140) and with antibodies to nuclear matrix protein (NXP)-2 (anti-MJ or anti-p140) [19,25-29].
High-risk patients have the following clinical features:
•Age >40 years at the time of IIM onset
•Features of persistent high disease activity despite immunosuppressive therapy (including relapse of previously controlled disease)
•Dysphagia (moderate to severe)
•Cutaneous necrosis or ulceration
●Intermediate risk – Anti-SAE, anti-HMGCR, anti-Mi-2, and anti-MDA5 were noted to confer an intermediate risk.
●Low risk – The myositis-specific autoantibody associations are anti-synthetase antibodies, anti-SRP, and myositis-associated antibodies including anti-RNP, anti-PM-Scl, anti-Ku. All of these autoantibodies appear to be associated with a decreased risk of malignancy but an increased risk of interstitial lung disease [25]. More study is required to determine the utility of these autoantibodies for cancer screening in patients with myositis.
Low-risk patients have the following clinical features:
•Raynaud phenomenon
•Inflammatory arthropathy
•Interstitial lung disease
APPROACH TO SCREENING —
In the absence of definitive data suggesting one approach over another, screening practices have historically varied among clinicians.
An expert panel formed a total of 18 final recommendations, which addressed idiopathic inflammatory myopathy (IIM)-associated cancer risk stratification (compared with the wider IIM population, not the general population), use of screening modalities, and screening frequency [24].
Positron emission tomography (PET) using [18F] fluorodeoxyglucose (FDG) and combined with computed tomography (FDG-PET/CT) is a highly sensitive imaging technique that has been used increasingly for the detection of malignancy, but few studies have examined its role in screening for malignancy in patients with dermatomyositis (DM) and polymyositis (PM) [30-32]. Further study is needed to determine whether FDG-PET/CT has a role is screening practices among patients with DM or PM. We do not perform routine PET scanning to screen patients with DM or PM for malignancy. Commercial insurances would not cover this indication in most cases.
If a very high index of suspicion remained after extensive standard investigation, PET scanning could be considered in a patient with myositis at very high risk for an underlying malignancy in the same way that it would be considered in a patient without inflammatory myopathy. The expert panel conditionally recommended this modality, specifically noting that clinicians should consider carrying out an 18F-FDG PET/CT scan for patients with adult-onset IIM at a "high risk of IIM-related cancer," where underlying cancer has not been detected by investigations at the time of IIM diagnosis and clinicians should consider carrying out an 18F-FDG PET/CT scan as a single screening investigation for patients with anti-transcription intermediary factor 1 (TIF1)-gamma antibody-positive DM with disease onset at age >40 years and with ≥1 additional "high-risk" clinical feature.
Post-treatment surveillance — The value of repeat cancer screening in patients with established PM and DM is not well-established. Most studies have shown an increased risk of cancer for at least five years in patients with DM (but not PM), although the risk declines annually (see 'Temporal relationship' above). Therefore, the diagnostic yield of continued surveillance for cancer after the initial screening is low, unless specific signs suggestive of an underlying malignancy appear, or a relapse of the inflammatory myopathy occurs after a period of remission [9]. Patients should continue to have routine, age-appropriate screening (eg, mammogram, pelvic exam) as in the general population. (See "Overview of preventive care in adults", section on 'Cancer screening'.)
IMPACT OF MALIGNANCY ON DISEASE SEVERITY —
The presence of a tumor does not appear to affect the severity or distribution of weakness, the duration of weakness prior to diagnosis, or the height of creatine kinase elevation. Myositis associated with cancer, however, responds more poorly to treatment than myositis in the absence of cancer, and survival rates are worse for patients with malignancy [33,34]. Poor response to myositis treatment therefore should raise the possibility of an underlying malignancy.
SUMMARY AND RECOMMENDATIONS
●Pathophysiology – Both dermatomyositis (DM) and polymyositis (PM) are idiopathic inflammatory myopathies associated with malignancies in a significant minority of cases. The close relationship between inflammatory myopathy and cancer is consistent with the concept that paraneoplastic processes linked to oncogenesis and autoimmunity contribute to the disease in a subset of DM and PM cases. (See 'Introduction' above and 'Pathophysiology' above.)
●Epidemiology – Population-based cohort studies from a number of countries have confirmed the increased risk of malignancy among patients with inflammatory myopathies. The cancer rates reported with PM are consistently lower than that of DM. (See 'Epidemiology' above and 'Incidence' above.)
●Types of malignancies – Adenocarcinomas of the cervix, lung, ovaries, pancreas, bladder, and stomach account for approximately 70 percent of the cancers associated with inflammatory myopathies. (See 'Types of malignancies' above.)
●Temporal relationship – Cancer can be diagnosed before, simultaneously with, or after the diagnosis of inflammatory myopathy. (See 'Temporal relationship' above.)
●Risk factors – Clinical factors associated with an increased risk of malignancy include older age at disease onset, dysphagia, evidence of capillary damage on muscle biopsy, cutaneous necrosis, cutaneous leukocytoclastic vasculitis, and Raynaud phenomenon. Patients with interstitial lung disease appear to have a lower frequency of malignancy. (See 'Risk factors' above.)
●Autoantibodies – Some serum autoantibodies in DM and PM confer a positive risk of malignancy, whereas others are associated with a negative risk. Cancer-associated myositis (CAM) in adults has been associated in several studies with antibodies to transcription intermediary factor (TIF)-1gamma (anti-p155, anti-p155/140) and antibodies to nuclear matrix protein 2 (NXP-2; anti-MJ or anti-p140). Conversely, the presence of myositis-specific (anti-synthetase antibodies, anti-SRP) and myositis-associated antibodies (anti-RNP, anti-PM-Scl, anti-Ku) appears to be associated with a decreased risk of malignancy but an increased risk of interstitial lung disease in DM. (See 'Serum autoantibodies' above.)
●Screening – All patients newly diagnosed with PM or DM should be evaluated for the possibility of an underlying malignancy. Most cancers will be found with a comprehensive history and physical examination, including a pelvic exam, along with the following investigations (see 'Impact of malignancy on disease severity' above):
•Complete blood count, liver function tests, urinalysis
•Fecal occult blood test, if screening colonoscopy not indicated
•Chest radiograph
•Age- and sex-appropriate Pap test, testicular self-examination, mammography, and colonoscopy
Further investigation, including CT scanning of the chest/abdomen/pelvis, is directed by abnormal results found on the above evaluation or should be undertaken in those patients assessed to be at high risk for an underlying malignancy (See 'Approach to screening' above.).
●Surveillance – The value of repeat cancer screening in patients with established PM and DM is not well-established. Most studies have shown an increased risk of cancer for at least five years in patients with DM (but not PM), although the risk declines annually. Patients should continue to have routine, age-appropriate screening (eg, mammogram, pelvic exam) as in the general population. (See 'Post-treatment surveillance' above.)
●Impact on severity – The presence of a tumor or does not appear to affect the severity or distribution of weakness, the duration of weakness prior to diagnosis, or the height of creatine kinase elevation. Myositis associated with cancer, however, responds more poorly to treatment than myositis in the absence of cancer. (See 'Impact of malignancy on disease severity' above.)
ACKNOWLEDGMENT —
The UpToDate editorial staff acknowledges Marc L Miller, MD, who contributed to an earlier version of this topic review.
