Efficacy and Tolerability of 5-Year Adjuvant Imatinib Treatment for Patients With Resected Intermediate- or High-Risk Primary Gastrointestinal Stromal Tumor

Three years of adjuvant imatinib mesylate therapy is associated with reduced recurrence rates and improved overall survival in patients with high-risk primary gastrointestinal stromal tumor (GIST) compared with patients who receive 1 year of treatment. The impact of a longer duration of therapy is unknown.To determine whether adjuvant treatment for primary GIST with imatinib for 5 years is tolerable and efficacious.This prospective, single-arm, phase 2 clinical trial (Postresection Evaluation of Recurrence-free Survival for Gastrointestinal Stromal Tumors With 5 Years of Adjuvant Imatinib [PERSIST-5]) included adult patients with primary GIST (expressing KIT) at 21 US institutions who underwent a macroscopically complete resection and were at intermediate or high risk of recurrence, defined as primary GIST at any site measuring 2 cm or larger with 5 or more mitoses per 50 high-power field or nongastric primary GIST measuring 5 cm or larger. Data were collected from August 5, 2009, through December 20, 2016.Imatinib, 400 mg once daily, orally for 5 years or until discontinuation of therapy because of progression or intolerance.The primary end point was recurrence-free survival (RFS). The secondary end point was overall survival.Of the 91 patients enrolled, 48 (53%) were men with a median age of 60 years (range, 30-90 years). Median tumor size was 6.5 cm (range, 2.3-30.0 cm). Median treatment duration was 55.1 months (range, 0.5-60.6 months); 46 patients (51%) completed 5 years of imatinib therapy. Estimated 5-year RFS was 90% (95% CI, 80%-95%), and overall survival was 95% (95% CI, 86%-99%). Recurrence was noted in 7 patients: 1 had disease recur while receiving imatinib (PDGFRA D842V mutation) and died; 6 had disease recur after discontinuation of imatinib therapy. Two additional deaths were unrelated to treatment or tumor progression. Forty-five patients (49%) stopped treatment early because of patient choice (10 [21%]), adverse events (15 [16%]), or other (11 [12%]). All 91 patients experienced at least 1 adverse event, and 17 (19%) experienced grade 3 or 4 adverse events.In this first adjuvant trial, to our knowledge, of patients with resected primary GIST who received 5 years of imatinib therapy, no patient with imatinib-sensitive mutations had disease recur during therapy. For patients in whom disease recurred, recurrence was within 2 years of discontinuation of imatinib therapy. Approximately half of the patients discontinued treatment early, most commonly because of patient choice, thus emphasizing the importance of close clinical monitoring to continue imatinib treatment for patients at appropriate risk.ClinicalTrials.gov identifier: NCT00867113.