Abstract
Gynecomastia refers to the abnormal enlargement of the male breast caused by the proliferation of the glandular component of the breast, typically due to sexual hormone disturbance. Multiple medications have been linked to the development of gynecomastia with varying incidences. This adverse event has also been associated with TKIs such as imatinib, dasatinib, and rarely nilotinib. However, it is poorly described and regarded as a rare event. Herein, we present the first case of a CML patient who developed gynecomastia after switching from imatinib to flumatinib. The patient is an 82-year-old male. He was diagnosed with CML and initially treated with imatinib. However, the treatment response milestone after three months of imatinib was not achieved. Hence, flumatinib was used to replace imatinib. Unexpectedly, two weeks later, he developed gynecomastia. Gynecomastia usually causes distress to patients, and there are currently no clear mechanisms or management strategies for this condition. Inspired by this case and through a review of the literature, we propose possible mechanisms and management strategies for this rare adverse event associated with TKIs, along with future perspectives. This may assist others in dealing with this issue and stimulate research on it.