Metaplastic breast carcinomas and their relationship with basal-like phenotype

Metaplastic carcinoma is a rare tumor showing high histological grade and low hormone receptor expression. It has pure epithelial and mixed types. Studies have suggested that metaplastic carcinomas may have a basal-like profile. Our aim was to evaluate the clinicopathological features of 11 metaplastic carcinomas and determine their resemblance to basal-like breast carcinomas regarding their morphological and immunohistochemical profile.

Eleven metaplastic carcinoma cases were reviewed for their histopathological features. All tumors but one were evaluated for the immunohistochemical expressions of the cytokeratin 5/6, cytokeratin 14 and epidermal growth factor receptor; and hormonal status was assessed.

Four of eleven cases were carcinoma with chondroid metaplasia, 3 were adenosquamous carcinoma, 2 were squamous cell carcinoma and 2 were carcinosarcoma. The mean patient age was 53 years and the mean tumor size was 5,1 cm. Histological grade was 3 for all with a nuclear grade of 3. Average mitotic count was 31/10 high power fields. Four cases had a central scar, 5 had central necrosis and 7 had geographic necrosis. Tumor growth pattern was pushing in 6 cases and no carcinoma in-situ was identified in 5 cases. Seven of 10 patients had axillary lymph node metastasis. Seven of 10 cases were triple-negative (estrogen receptor-, progesterone receptor-, HER2-) and 6 of them were positive for cytokeratin 5/6 and/or epidermal growth factor receptor, consistent with basal-like immunophenotype. Cytokeratin 14 was positive in 7 cases.

Metaplastic carcinomas are large-sized, high-grade tumors with prominent nuclear pleomorphism and frequent mitosis. They rarely overexpress hormone receptors and HER2 and generally have basal-like immunophenotype.