Metaplastic carcinomas of the breast without evidence of epithelial differentiation: A diagnostic approach for management.

AIMS Although rare, malignant sarcomatoid breast tumours without evidence of epithelial differentiation comprise a diagnostic challenge with management implications. Earlier studies have generally considered these to be primary breast sarcomas; however, supporting evidence is lacking and management remains variable. This study aimed to provide an evidence-based approach to improve consistency of diagnosis and management for such cases. METHODS AND RESULTS A large series (n=140) of metaplastic breast carcinoma (MBC) diagnosed in Nottingham over 18 years was analysed. Only cases with available data on immunohistochemical expression of cytokeratins (CKs) were included. The prevalence and pattern of expression for various CKs were assessed and details of tumours negative for CKs were collected. A diagnostic approach based on our experience is provided. 47 cases (34%) showed foci of conventional type invasive breast carcinoma or DCIS, whereas 93 cases (66%) were diagnosed as MBC based on morphology and/or CK expression. 97 cases (69%) were negative for one or more CKs, with 18 cases (13%) negative for 5 or more CKs. 8 cases (6%) lacked expression of all CKs tested. Further examination showed evidence of carcinomatous nature in 5 cases, whereas 3 were diagnosed as MBC following extensive diagnostic workup and on our experience. CONCLUSION This study suggests that MBC represent a spectrum of neoplasms with some lacking CKs expression. Sarcomatoid neoplasms of the breast lacking evidence carcinomatous morphology and CK expression may represent an extreme end of differentiation that can be considered as carcinomas rather than sarcomas for management purposes (following extensive workup).