Breast involvement of Adult T-cell leukemia-lymphoma (ATLL) is extremely rare, and the data on the characteristics are limited. We herein describe a 49-year-old woman who presented with skin involvement of ATLL. Positron emission tomography/computed tomography showed bilateral breast lesions. Although the patient once achieved a complete metabolic response, a relapse of her ATLL occurred. The patient received subsequent allogeneic hematopoietic stem cell transplantation (HSCT). To our knowledge, only four cases of ATLL with breast involvement have previously been reported, and the prognoses have generally been poor. Breast lesions of ATLL have aggressive features, and intensive systemic chemotherapy and HSCT are required to improve survival.