Cost-effectiveness of three years of adjuvant imatinib in gastrointestinal stromal tumors (GIST).
137 Background: Recent clinical trial data have demonstrated that 3 years (yr) of adjuvant imatinib therapy for patients with surgically resected GIST leads to a significant improvement in recurrence free survival and overall survival vs. 1 yr of therapy. The objective of this study is to assess cost-effectiveness of treating with 3 yrs vs. 1 yr of adjuvant imatinib in the US from a payer’s perspective. Methods: A Markov model was developed to predict GIST recurrence, treatment (txt) costs, and quality-adjusted survival over a lifetime horizon. Patients transitioned between 3 health states: recurrence free GIST, GIST recurrence, and death. Monthly recurrence and mortality rates for 3 yr and 1 yr imatinib were derived from SSGXVIII/AIO clinical trial. The 5-yr recurrence rate observed in the trial was extrapolated for the remaining duration of the model horizon. First recurrence after active txt was treated with imatinib 400mg daily (800mg daily if recurrence during active txt). For subsequent disease progression, patients were treated with imatinib 800mg, sunitinib or best supportive care. After 5 years, txt specific mortality rate was applied for patients with recurrence. Costs and utilities were derived from published literature. Expected costs and quality-adjusted life years (QALYs) were estimated for each txt strategy. Costs and QALYs were discounted at 3% per yr. Extensive sensitivity analyses were conducted. Results: Total lifetime cost per patient was $302,100 with 3 yrs vs. $217,800 for 1 yr of imatinib therapy. Patients on 3 yrs of imatinib had higher QALYs (8.53 vs 7.18) vs. 1yr of imatinib. Incremental cost effectiveness ratio of 3 yrs of imatinib vs 1 yr of imatinib was $62,600/QALY. Model results were sensitive to rate of GIST recurrence beyond 5 yrs and monthly cost of adjuvant imatinib. At a threshold of $100,000/QALY, 3 yr imatinib therapy was cost-effective in 100% of simulations vs. 1 yr of imatinib. Conclusions: Model results suggest that treating patients with 3 yrs of imatinib is cost-effective vs. 1 yr of imatinib below the widely used $100,000/QALY threshold. Both clinical and economic results suggest treating surgically resected GIST patients with 3 yrs of imatinib would result in improved quality-adjusted and overall survival.