Pyoderma gangrenosum (PG) is a rare, ulcerative, and painful neutrophilic dermatosis of unknown cause associated with systemic diseases and/or pathergy phenomenon in 30% of cases. We report the case of a breast cancer patient submitted to oncoplastic conservative surgery followed by adjuvant radiotherapy, with long-term progression to PG. It’s rare and challeng ing nature reinforces the need for early diagnosis to increase treatment effectiveness and reduce morbidity.