INTRODUCTION: Sebaceous carcinoma (SC) is a malignant neoplasm differentiated from the mature sebocyte and occurs mainly in the periorbital area. However, SC of the breast is extremely rare. We report a case of sebaceous breast carcinoma in a Japanese man with a CASE PRESENTATION: A 77-year-old Japanese man had been aware of a mass in his right breast for about a year and had visited his previous physician for a follow-up. Over the next year, the mass grew, and the last doctor he visited referred him to our hospital for further examination and treatment. Physical examination revealed a palpable 3-cm-large mass of the right breast. There was no skin invasion, and core needle biopsy revealed invasive ductal carcinoma cT2N1M0 cStage IIB, estrogen receptor (+)/progesterone receptor (+)/HER2/ CONCLUSIONS: The prognosis of SC of the breast has not been elucidated. As cases of SC with a