Sustained erythrocytosis due to the use of Lenvatinib.

Erythrocytosis has previously been described with sunitinub, sorafenib and pazopanib. The exact mechanism of this phenomenon is not known. It might increase the risk of venous and arterial thromboses in cancer patients that are already in a hypercoagulable state due to cancer itself. In addition, laboratory work-up for polycythemia may prove extensive and costly. Therefore, clinicians need to be aware of this important side effect of tyrosine kinase inhibitors.