Sunitinib Causes Macrocytosis in Patients with Advanced Renal Cell Carcinoma

Background: Sunitinib is approved for treatment of advanced renal cell carcinoma (RCC). Based on a clinical observation that patients receiving sunitinib developed macrocytosis, we undertook a study to further define this observation. Methods: In a retrospective review of RCC patients treated at a single centre, data on treatment duration, hematology parameters, concomitant medications, vitamin B₁₂ and folate levels, and thyroid function were recorded. Results: The 43 patients reviewed had received a median of 5 cycles of sunitinib. Overall, 21 patients (49%) developed macrocytosis after a median of 3 cycles. Of the 9 patients that received 2 or fewer cycles, none developed macrocytosis. Among patients with macrocytosis, 9 (43%) had anemia at the time macrocytosis was first documented. In patients who did not develop macrocytosis, 82% showed a trend of increasing mean corpuscular volume. Conclusions: Treatment with sunitinib in patients with rcc can cause macrocytosis. The frequency of macrocytosis increases with duration of treatment. The mechanism of sunitinib-associated macrocytosis remains to be elucidated.