Understanding Low-Grade Fibromatosis-Like Metaplastic Breast Carcinoma, a Tertiary Care Center Experience: Case Series and Review of Literature

Low-grade fibromatosis-like metaplastic breast carcinoma is a rare and challenging subtype of breast carcinoma due to its distinctive histological features mimicking a variety of lesions varying from benign to malignant, underscoring the importance of accurate diagnosis. We evaluated the clinicoradiological, histopathological features, and immunohistochemical profile of 11 low-grade fibromatosis-like metaplastic breast carcinoma patients diagnosed at our tertiary care center. Median age at diagnosis was 67 years (range 47-76 years) with a palpable breast lump of 1 to 2 years duration. Histologically, besides classical fibromatosis-like pattern, nodular growth was also noted (<i>n</i> = 2). Cytologically, spindle cell and stellate morphology were observed in 3 tumors each while rest of the tumors showed both features. Cellularity was minimal in 2, moderate in 8 and high in 1 tumor with mild to moderate nuclear atypia. Two tumors had small foci of infiltrative epithelial nests. Mixed inflammatory infiltrate was seen in all tumors. On immunohistochemistry, the tumor cells demonstrated positive staining for AE1/AE3, keratin 5/6, SMA, and p63, while negative for other markers. Details of initial treatment were available in 9 patients, of which 3 developed metastases. Low-grade fibromatosis-like metaplastic breast carcinoma is a rare and distinct subtype of metaplastic breast cancer with unique histological features and heterogeneity in morphology, posing diagnostic challenges and should be diagnosed after meticulous clinicopathological evaluation, comprehensive sampling and extensive immunohistochemistry panel.