Objective: There is a wide variability in the pharmacokinetics, pharmacodynamics and tolerance of anticancer drugs based on ethnicity. GIST is a rare cancer, (~1% of GI cancers). Imatinib is used in the neo-adjuvant, adjuvant and metastatic setting. Methods: The purpose of this study was to report the difference in hematologic toxicities to imatinib among different ethnicities when treated for GIST either in the adjuvant or metastatic setting. Results: Among 57 patients (median age 61 years, M:F = 41:16(F); ethnicities: White 65%, African-American (AA 19%, Asian 12% and Hispanic 3%), neutropenia (Grade 3 & 4) was seen in 6 patients (10%): 5 AA and 1 Asian. 45% of all AA patients developed neutropenia. Median absolute neutrophil count (ANC) nadir was 700/µL, median duration on drug prior to onset of neutropenia was 4.5 weeks and median duration of neutropenia was 4 weeks. One patient developed febrile neutropenia. Dose interruptions were needed in 3, dose-reductions in all patients, and 3 patients required pegfilgrastim. One patient had to discontinue imatinib, while one patient was escalated back to 400mg daily dose. Conclusions: This is the first study to examine ethnic variations in myelosuppression following imatinib in patients with GIST. Keywords: Gastrointestinal stromal tumors, imatinib, ethnicity, neutropenia, anemia
Corresponding Author: Saif M.