Macrocytosis and Cobalamin Deficiency in Patients Treated with Sunitinib

To the Editor: Sunitinib malate is a multitargeted tyrosine kinase inhibitor approved for the treatment of advanced renal-cell carcinoma. We report on an asymptomatic increase in the mean corpuscular volume of erythrocytes and cobalamin deficiency in six patients with metastatic renal-cell carcinoma who were treated for more than 5 months with sunitinib as part of a clinical trial evaluating the efficacy and safety of continuous daily administration of the drug. The starting dose of sunitinib was 37.5 mg daily; three patients required a dose reduction to 25 mg, and one patient had a dose escalation to 50 mg daily. An . . .