Fibromatosis (desmoid tumor) of the breast mimicking a case of ipsilateral metachronous breast cancer

Background: Fibromatosis or desmoid tumor of the breast is an extremely rare entity. While it lacks a metastatic potential, it can grow aggressively in a locally infiltrating pattern. The failure to recognize this as a finite entity within the breast can lead to local recurrence after incomplete excision. Case presentation: We report a case of a 70 year old patient with a remote history of invasive breast cancer (treated twelve years earlier by lumpectomy, axillary lymph node dissection, postoperative radiation therapy, and five years of tamoxifen) who developed fibromatosis within another quadrant of the same breast that clinically, mammographically, and sonographically mimicked that of the development of an ipsilateral metachronous breast cancer. After the initial diagnosis of fibromatosis was made on a minimally invasive ultrasound guided biopsy, it was successfully treated by wide local excision. Conclusion: After appropriate recognition, wide local excision can be the appropriate surgical management strategy for fibromatosis of the breast.