Macrocytosis during sunitinib treatment predicts progression-free survival in patients with metastatic renal cell carcinoma

Sunitinib, a multi-targeted receptor tyrosine kinase inhibitor, is a first-line treatment for metastatic renal cell carcinoma (mRCC) in patients in 'low' and 'intermediate' Memorial Sloan Kettering Cancer Center and Heng risk groups. Disruptions of hematopoiesis, such as anemia, neutropenia, and thrombocytopenia, are typically observed during sunitinib treatment. When it comes to RBC parameters, an increase in mean cell volume (MCV) tends to occur, meeting the criteria for macrocytosis in some patients (MCV > 100 fL). We examined changes in RBC parameters of 27 mRCC patients treated with sunitinib (initial dose of 50 mg/day, 6-week treatment: 4 weeks on, 2 weeks off) and correlated them with progression-free survival time (PFS). Patients who had macrocytosis after 3 treatment cycles had significantly longer PFS than those whose MCV stayed less than 100 fL (not reached vs. 11.2 months, p < 0.001). We also found a correlation between MCV values after the first and third treatment cycles and the risk of progression: HR of 0.9 (0.81-0.99) and 0.76 (0.65-0.90) per 1 fL increase in MCV, respectively. The mechanism of MCV elevation during sunitinib treatment has not yet been fully explained. One of the probable causes is sunitinib's inhibitory influence on c-Kit kinase, as is the case with imatinib. For mRCC patients, this phenomenon could help predict PFS, but since our sample was small, further studies are essential.