[A case of locally recurrent breast cancer difficult to differentiate from nodular fasciitis]

Breast-conserving surgery was performed on a 78-year-old woman for left breast cancer 5 years previously (invasive ductal carcinoma, T1cN2M0, stage IIIA, ER[+], PR[-], HER2[-]). Chemotherapy, radiotherapy, and hormonal therapy were administered. A left subclavian tumor was detected, and an excisional biopsy was performed. Histological examination showed spindle cells, different from primary breast cancer histology, and nodular fasciitis was diagnosed negative cytokeratin and vimentin immunostaining results. After 12 months, a mass had developed in the same region, and reoperation was performed for resection. Similar spindle cells were observed, but they tested positive for cytokeratin. Carcinoma was diagnosed and thought to be locally recurrent breast cancer. Despite postoperative chemotherapy, the patient experienced bone and lung metastasis and a third local recurrence. She died 13 months following the last surgery. Recurrent breast cancer sometimes displays different histology from the initial cancer, and mimics stromal tumors in certain cases.