BACKGROUND

Imatinib mesylate, an orally administered kinase inhibitor that targets the Kit (CD117) protein, currently has 10 approved indications including treatment of chronic myelogenous leukemia and metastatic gastrointestinal stromal tumors (GIST). Treatment with adjuvant imatinib following surgical resection of localized Kit-positive GIST, the most recent FDA-approved indication (December 2008), has been shown to significantly improve recurrence-free survival (RFS) compared with surgical resection alone. Although adjuvant imatinib has proven effective in clinical trials, it is important to consider the economic impact to health plans of introducing imatinib in accordance with its new labeled indication.

OBJECTIVE

To evaluate the budgetary impact over a 3-year time horizon of treating patients with localized Kit-positive GIST with 1 year of adjuvant imatinib following surgical resection.

METHODS

A Markov model was developed to predict patients' transitions across health states defined by initial treatment (surgical resection followed by adjuvant imatinib 400 milligrams [mg] daily versus surgical resection alone), recurrence, and progression. Treatments for a first recurrence were (a) imatinib 400 mg daily for recurrences following resection only or after completion of 1 year of treatment with imatinib 400 mg daily and (b) imatinib 800 mg daily for recurrence during active treatment with imatinib 400 mg daily. Treatments for further progression were imatinib 800 mg daily, sunitinib, or best supportive care (BSC) following imatinib 400 mg per day, and sunitinib or BSC following imatinib 800 mg daily. Recurrence rates were derived from the American College of Surgeons Oncology Group (ACOSOG) Z9001 clinical trial, which compared 1 year of adjuvant imatinib following surgical resection with surgical resection only. The total number of patients with localized and surgically resected GIST (incidence rate of 0.36 per 100,000) was estimated from epidemiologic studies of GIST. Uptake of treatment with imatinib was estimated from unpublished data from qualitative market research funded by the study sponsor. The uptake rate assumptions reflected both (a) the percentage of patients with Kitpositive disease and (b) the percentage of clinically eligible patients who would use imatinib. Costs were estimated by combining unit costs from published sources with expected resource utilization based on the clinical trial publication and National Comprehensive Cancer Network guidelines on the treatment of patients with GIST. To obtain estimates of the budgetary impact, we compared estimated health care costs with versus without adjuvant imatinib, where health care costs with imatinib reflected the costs of treatment minus cost offsets associated with delayed or avoided recurrence or progression. All "with" scenarios assumed no additional uses other than surgically resected localized Kit-positive GIST (i.e., no change in off-label use of imatinib). The budgetary impact was estimated for the first 3 years after the introduction of adjuvant imatinib in accordance with its new labeled indication in a hypothetical plan population of 10 million persons. Results were calculated both as total budgetary impact and as per member per month (PMPM) cost in 2009 dollars. Sensitivity analyses were performed to test the robustness of model results to changes in parameter estimates.

RESULTS

The model predicted 36 incident resected GIST cases per year in a health plan of 10 million members. The estimated counts of cases treated with adjuvant imatinib were 10.8, 16.2, and 21.6 in the first, second, and third years after introduction, respectively, with the annual increases attributable to changes in the proportion of patients with resected GIST assumed to use imatinib (30% in year 1, rising to 45% in year 2 and 60% in year 3). The model predicted that treatment of these cases with imatinib will increase pharmacy costs by an additional $505,144 in the first year, $757,717 in the second year, and $1,010,289 in the third year. Increased resource use associated with monitoring patients during and after treatment with adjuvant imatinib would cost an additional $21,564, $38,145, and $56,605 in the first, second, and third years, respectively. Recurrence would be avoided or delayed in 7 patients over the 3-year period. Avoided or delayed recurrences would result in cost offsets of $61,583 in the first year, $156,702 in the second year, and $233,849 in the third year. The net budgetary impact was estimated to be $465,126 in the first year (less than $0.01 PMPM), $639,159 in the second year ($0.01 PMPM), and $833,044 in the third year ($0.01 PMPM). Results of sensitivity analyses indicated that the budgetary impact in the third year is most sensitive to changes in the price of adjuvant imatinib and recurrence rates.

CONCLUSIONS

The model predicted that the introduction of adjuvant imatinib for treatment of surgically resected, localized, Kit-positive GIST will lead to a net budgetary impact of $0.01 PMPM in the third year after introduction assuming change in use only in accordance with the new labeled indication. Approximately 11.7%-21.9% of the cost of adjuvant imatinib is offset by the reduction in costs associated with GIST recurrence.