[Metaplastic carcinomas of the breast: a morphological and immunohistochemical study].

Introduction: Metaplastic carcinomas of the breast are rare and form a heterogenic group of tumors, characterized by the presence of squamous or sarcomatoid differentiation.

Patient And Methods: In 23 cases, we study the main histoprognostic features, hormonal status, and the expression of HER2, CK5/6, CK14, p63, EGFR, beta-catenin, MUC1 and E-cadherin, the expression of this seven last antigens being also studied in nodal metastases.

Results: The different metaplastic types are spindle cell carcinoma (35%), squamous cell carcinoma (26%), osteo- or chondrosarcomatoid (11%) or mixed type (26%). Vascular emboli are seen in 30% of the tumors and perinervous infiltration in 4%. 33% of the patients have nodal metastases. The immunohistochemical features are: RO+: 4%; RP+: 8%; HER2+: 0%; p63+: 74%; CK14+: 83%; CK5/6+: 74%; EGFR+: 100%; E-cadherin+: 70%; beta-catenin: aberrant staining (cytoplasm or weak membrane staining greater than 5%): 74%, negative: 13%; MUC1: aberrant staining (cytoplasm or complete membrane staining greater than 5%): 35%, pure partial membrane staining: 22%, negative: 43%. In 43% of tumors, more aberrant staining for MUCI is present in nodal metastases compared with primitive tumor.

Conclusion: Metaplastic carcinomas are aggressive tumors, generally with a "triple-negative" and basal phenotype. The expressions of MUC1 and beta-catenin are often absent or aberrant, which could favor metastatic dissemination.