Metaplastic carcinoma masquerading as fibromatosis: A diagnostic dilemma

Metaplastic breast carcinoma (MBC) is a rare, heterogeneous group of neoplasm of breast, accounting for about 0.2-1% of all invasive breast carcinomas. Its variants include low grade adenosquamous carcinoma, fibromatosis like metaplastic carcinoma, spindle cell carcinoma, squamous cell carcinoma and mixed metaplastic carcinoma. We report a case of a 48 year old female, who presented with painful lump in lower inner quadrant of right breast since one and half month, gradually increasing in size. Trucut biopsy was reported as Fibromatosis of breast. Excisional biopsy was consistent with malignant spindle cell lesion, Fibromatosis like-Metaplastic carcinoma (FLMC). Right modified radical mastectomy with axillary lymph node dissection was diagnosed as FLMC, Stage pT4N0. In literature, only 68 cases of FLMC are reported in the last 20 years. FLMC is a newly- described MBC because of their resemblance to pure fibromatosis. The diagnosis is potentially challenging because of the morphologic overlap with other low-grade spindle cell lesions. Extensive grossing and histopathological examination with immunohistochemistry markers is essential for arriving at a conclusive diagnosis.