Investigation of Regorafenib-induced Hypothyroidism in Patients with Metastatic Colorectal Cancer.

Hypothyroidism is one of the side-effects caused by regorafenib. In the Japanese subset of the CORRECT study, hypothyroidism developed in 1.5% of the patients, but was not grade 3 or higher in any patient. Regorafenib is an oral multi-kinase inhibitor that has the same mechanism of action as sunitinb. However, the reported incidence of sunitinb-related hypothyroidism varies widely, ranging from 16.0% in clinical trials to 35.4% in post-marketing surveillance studies. In general, symptoms of hypothyroidism include fatigue and dysphonia. Hyperthyroidism must, therefore, be appropriately managed in order to maintain patient quality of life and avoid a critical level of hypothyroidism. During the first cycle of treatment with regorafenib, the incidence of abnormal thyroid-stimulating hormone (TSH) elevation was 31.4%. Our results suggest that thyroid function tests should be performed from day 1 of treatment with regorafenib. It would be prudent to consider routine monitoring of thyroid function in all patients who receive regorafenib and to recommend endocrinological consultation as necessary.