Dermatofibrosarcoma protuberans is a rare cutaneous soft tissue neoplasm with the potential for intermediate malignancy, and is characterized by local invasion and recurrence. It can occur at almost any site, but usually arises in the trunk and extremities. Dermatofibrosarcoma protuberans mimicking a primary breast lesion has not previously been reported in Korea. We report on the case of a 28-year-old female patient with dermatofibrosarcoma protuberans on one of her breasts, which is a very unusual site.