Effectiveness of adjuvant imatinib in patients with gastrointestinal stromal tumor: Results of a population-based, matched-cohort study

Objective: Data are limited on the use of adjuvant imatinib in patients with gastrointestinal stromal tumor (GIST) outside of clinical trials. This retrospective, population-based, matched-cohort study evaluated adjuvant imatinib treatment patterns, assessed impact on clinical outcomes, and estimated effectiveness based on number needed to treat (NNT). Research design and methods: GIST-related claims from the PharMetrics claims database were included (20002010). A stepwise identification algorithm identified appropriate patients based on GIST-related ICD-9-CM codes, who were classified as 'imatinib (IM) patients' receiving imatinib within 84 days post-surgery and 'non-imatinib (non-IM) patients' undergoing surgery but not receiving imatinib during the study period. The primary composite outcome was based on incidence of a second GIST-related surgery and long-term follow-up in the matched cohorts. IM patients were matched with up to eight non-IM patients on age, gender, ICD-9-CM code, and first surgery date. Results: A total of 118 IM and 4088 non-IM patients with possible GIST ICD-9s and surgery were included. The median duration between first and second surgeries was significantly longer in IM than non-IM patients (488vs. 290 days; p0.0005). IM patients also had longer median follow-up from initial surgery to composite outcome (433vs. 320 days; p0.002). Adherence to IM, measured by medication possession ratio, was 0.83 and 0.73 during the first and second years of treatment, respectively. IM patients were less likely to have the composite outcome compared with non-IM patients (hazard ratio0.501; p0.0005). The NNT to prevent one outcome was 4. Conclusions: Patients receiving adjuvant imatinib treatment were less likely to have second surgery or be lost to follow-up, and had a longer interval to second surgery. Although treatment with adjuvant imatinib in patients with primary GIST is effective, adherence to imatinib and treatment duration are less than recommended by current treatment guidelines.