Breast Desmoid-Type Fibromatosis Mimicking Carcinoma on Imaging: A Case Report

Desmoid-type fibromatosis of the breast is a rare, locally aggressive fibroblastic tumor that lacks metastatic potential but demonstrates infiltrative growth and a tendency for local recurrence. Because its imaging characteristics often resemble those of breast carcinoma, establishing a preoperative diagnosis can be challenging.

A 57-year-old woman was referred after screening mammography detected a spiculated, high-density mass in the right breast. Ultrasonography demonstrated an irregular hypoechoic mass measuring approximately 36 mm in the upper inner portion of the breast with peripheral vascularity, findings suspicious for malignancy. Core needle biopsy revealed proliferation of spindle-shaped cells with minimal atypia and nuclear β-catenin positivity, suggesting desmoid-type fibromatosis. Tumor excision was subsequently performed for definitive diagnosis and local control. Histopathological examination confirmed desmoid-type fibromatosis with infiltrative growth into the surrounding adipose tissue. Focal margin involvement was identified, and the patient has been managed with careful follow-up.

Breast desmoid-type fibromatosis is a rare tumor that can closely mimic breast carcinoma on imaging studies. Histopathological evaluation is essential for establishing the diagnosis. Because positive surgical margins have been associated with an increased risk of local recurrence, careful postoperative follow-up is warranted.