Adjuvant therapy for localized, resected gastrointestinal stromal tumors

GIST: gastrointestinal stromal tumor; EUS: endoscopic ultrasound; AFIP: Armed Forces Institute of Pathology; HPF: high-power fields.

* Assessment of tumor mutational status is advised for all patients with GIST who are being evaluated for adjuvant therapy. However, we often do not obtain mutational testing in patients with smaller GISTs (eg, 0.5 mm to 2 cm) and low mitotic rate who undergo complete resection; these patients are typically observed and mutational testing does not alter management. Refer to UpToDate content on clinical presentation and diagnosis of GIST.

¶ Surveillance is preferred over adjuvant therapy for patients with tumors that are PDGFRA D842V positive and those that are KIT and PDGFRA wildtype; these are typically resistant to imatinib and may harbor certain mutations (eg, SDH deficiency, NF1, BRAF V600E, NTRK, and FGFR).

Δ Patients with no-, very low-, or low-risk tumors do not require follow-up, although they should be informed that recurrences are still possible and surveillance imaging is available. Posttreatment surveillance is appropriate for most other groups.

◊ Patients with high-risk tumors who tolerate treatment may choose to remain on imatinib for a total of five years or longer. In patients treated with adjuvant imatinib for up to three years, disease recurrence has been reported within 6 to 12 months of stopping treatment, suggesting that imatinib may maintain tumor dormancy rather than eradicate microdeposits.

§ For patients with intermediate-risk disease, we suggest adjuvant therapy for a minimum of three years, after an informed discussion about the benefits and risks of this approach. Those who decline or are ineligible for adjuvant therapy are offered posttreatment surveillance.

¥ Patients with a KIT exon 9 mutation demonstrate some relative resistance to imatinib, and we suggest higher doses of imatinib (800 mg daily rather than 400 mg daily), although data are limited for this approach in the adjuvant setting.

‡ Patients with other anatomic primary sites (esophagus, mesentery, peritoneum) or those with limited data follow the risk stratification of jejunum/ileum tumors.

† Mitotic rate is counted in an area of 5 square millimeters (mm²) on the glass slide section. For older microscopes with traditional field size optics, 50 HPF is equivalent to 5 mm². For modern microscopes with wider 40× lenses/fields, 20 HPF is equivalent to 5 mm². If necessary, the field of view should be measured to determine the actual number of HPF required to cover a 5 mm² area.^[1]

** Small number of cases.