Fibromatosis-Like Metaplastic Carcinoma of Breast: A Clinicopathological Study of 6 Patients.

Fibromatosis-like metaplastic carcinoma (FLMC) of breast is a rare neoplasm that exhibits distinct low-grade cytomorphology, a tendency for local recurrence and a favorable prognosis. This retrospective study aimed to evaluate the clinicopathological and immunohistochemical features of FLMC and assess its clinical behavior. Six female patients with histologically confirmed FLMC were included. Hematoxylin and eosin-stained slides were reviewed, and immunohistochemistry for keratin AE1/AE3, keratin CAM5.2, keratin 5/6, p63, EMA, ACTA1, desmin, and CD34 was performed. The mean age was 57.3 years, and all patients presented with a painless breast mass. Tumors were firm, unencapsulated, and averaged 4.9 cm in size on gross examination. Microscopically, they showed bland spindle cells in fascicular and storiform patterns with infiltrative borders. All tumors were positive for keratin AE1/AE3, keratin CAM5.2, and p63. EMA was positive in 1/3 tumors, keratin 5/6 in 3/3, ACTA1 in 2/3. All tumors were negative for desmin and CD34. No nodal metastasis was identified. On follow-up, one patient developed bone metastasis after 2 years, while the others remained disease-free 3 years post-surgery. FLMC is a rare low-grade epithelial malignancy that can mimic benign spindle cell lesions, making immunohistochemistry essential for diagnosis. Complete surgical excision with clear margins is curative in most patients.