Male breast cancer accounts for approximately 1% of the overall incidence of breast cancer. We report a rare case of intraductal papilloma(intracystic papilloma)in a 73-year-old man, which was suspected to be breast cancer as it presented as an approximately 6 cm mass below the left nipple in various imaging studies. The patient was aware of a mass measuring a few millimeters below the left nipple for 5 years, but had not sought treatment. He visited our department 3 months after redness and pain were noted around the nipple; the mass had enlarged. Palpation revealed a 6 cm smooth-surfaced mass as well as nipple retraction; diagnostic imaging showed a cystic tumor with a solid internal structure. Fine-needle aspiration cytology and core needle biopsy did not indicate a definitive diagnosis, and a left mastectomy and sentinel lymph node biopsy were performed based on a preoperative diagnosis of breast cancer. Pathological examination confirmed the diagnosis of intraductal papilloma, based on findings such as infarction-induced hemorrhagic necrosis, stromal and epithelial proliferation, apocrine metaplasia, and squamous epithelial metaplasia. Reports of a large-diameter intraductal papilloma(intracystic papilloma)suspicious for breast cancer in men are rare; therefore, surgical resection and detailed histopathological exploration of the whole tumor were required.