Gynecomastia in Male Patients Treated with Asciminib for Chronic Myeloid Leukemia: Two Case Reports

Background and Clinical Significance: Gynecomastia is not considered as an expected adverse event in patients treated by asciminib. We provide the first detailed description of this occurrence. Case presentation: Two elderly patients treated with asciminib for chronic myeloid leukemia—in the third-line setting for 6 months and in the second-line setting for 3 months, respectively, experienced gynecomastia. Both exhibited hormonal disturbances, with elevated follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, along with low serum total testosterone and increased prolactin levels in one. Imaging was performed in one patient and ruled out breast and testicular cancer. In both cases, advanced age, renal insufficiency and long-lasting exposure to previous tyrosine kinase inhibitors were confounding factors, but chronological arguments were in favor of an adverse effect of asciminib. The temporary discontinuation of asciminib in one patient and local treatment with androstanolone in both alleviated symptoms. The optimal response of CML was acquired and maintained, which allowed a later dose reduction in one case. Conclusions: Pathophysiological mechanisms are discussed but remain uncertain and probably multifactorial. Possible management options are presented.