Metastatic Male Breast Cancer Responding to Abemaciclib and Letrozole

What happened, in summary

A 65-year-old man sought care in June 2023 after a right breast growth had enlarged over about 3 years and recently developed ulceration and bleeding. Imaging showed a very large breast and chest-wall tumor with metastatic lymph-node and soft-tissue disease. Initial pathology was mistaken for Merkel cell carcinoma, but further review confirmed poorly differentiated invasive ductal breast cancer. The cancer was Stage IV, strongly estrogen-receptor positive, progesterone-receptor negative, and HER2-negative.

Once the breast-cancer diagnosis was established, he started letrozole plus abemaciclib. The treatment was well tolerated, and he reported no meaningful side effects. Clinically, the involved skin and tumor area became softer. Follow-up imaging in January 2024 showed clear shrinkage of the primary tumor, lymph nodes, and thoracic soft-tissue metastases. Newly visible sclerotic bone lesions were interpreted as healing changes rather than progression.

Imaging again showed no progression in July 2024. At his last documented visit in September 2024, he remained in good clinical condition and reported that treatment had not reduced his quality of life. The overall cancer response was a partial remission.