Characteristics of early-onset hematotoxicity of sunitinib in Japanese patients with renal cell carcinoma.

Background: A high incidence of severe hematological adverse events during sunitinib treatment complicates decision making on dose and treatment cycle. We identified the characteristics of early-onset hematotoxicity of sunitinib in Japanese patients with renal cell carcinoma (RCC).
Methods: Seventy-nine patients were treated with sunitinib as 6-week cycles of "4-week on 2-week off" schedule. To evaluate early-onset hematotoxicity, we compared patients with dose reduction during the first cycle (dose-reduced group, n = 57) and those who maintained the initial dose (dose-maintained group, n = 22). ABCG2 and FLT3 genotypes were analyzed for association between hematotoxicity and reported gene polymorphisms.
Results: Mean relative dose intensity (RDI) was similar in the two groups during the first 2 weeks of dosing in the first cycle, but was significantly lower in the dose-reduced group during the last 2 weeks. Lymphocytopenia and thrombocytopenia were observed in the dose-reduced group within the first 2 weeks. Genetic analysis indicated a significantly higher frequency of FLT3 738 T/C polymorphism in the dose-reduced group, but no significant difference in the ABCG2 421 C/A polymorphism.
Conclusions: This study showed a high incidence of sunitinib-induced hematotoxicity in Japanese patients with RCC, many of whom need dose adjustment during the first cycle. Further studies should verify whether dose adjustment based on early-onset thrombocytopenia prolongs sunitinib treatment.