Sustained erythrocytosis due to the use of Lenvatinib

Introduction Tyrosine kinase inhibitors have become the mainstay of treatment for many malignancies, but their use can be accompanied by unusual and often puzzling side effects. Case report We describe herein a 64-year-old patient who developed a robust and sustained erythrocytosis shortly after starting treatment with lenvatinib. Our patient also experienced elevated blood pressure, mucositis, and hand-foot syndrome that are not uncommonly seen with this agent. The clinico-laboratory work-up suggested that lenvatinib was the likely culprit in this case. Management & Outcome Lenvatinib had to be discontinued due to suboptimal tolerance and a short-lived response. With the discontinuation of lenvatinib, hemoglobin trended downwards and subsequently resolved. A score of 6 on the Naranjo nomogram supported a probable causality relationship between lenvatinib and the observed erythrocytosis. Discussion 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.