Metaplastic breast cancer: histologic characteristics, prognostic factors and systemic treatment strategies

Table 1 World Health Organization histologic classification of metaplastic breast cancer

Epithelial type metaplastic breast cancer	Histologic features
Squamous cell carcinoma	Infiltrating squamous carcinoma with polygonal cells, eosinophilic cytoplasm and possible keratin pearl formation.
Adenocarcinoma with spindle cell differentiation	Poorly cohesive sheets of predominant spindle cell morphology; resembles a low grade sarcoma.
Adenosquamous carcinoma	Glands display varying degrees of squamous differentiation, characterized by pavement-like architecture, prominent intercellular bridges and, to a lesser extent, keratin formation.
Mixed-type metaplastic breast cancer	Histologic features
Carcinoma with chondroid metaplasia	Immunoreactive for S-100, patchy for cytokeratin while being negative for smooth muscle antigen.
Carcinoma with osseous metaplasia	Infiltrating carcinoma with osseous differentiation of the mesenchymal component.
Carcinosarcoma	Infiltrating carcinoma with a malignant mesenchymal component.

Adapted from Tavassoli FA, Devilee P: World Health Organization classification of tumors: tumors of the breast and female genital organs. Pathology and genetics of tumors of the digestive system. In World Health Organization Classification of Tumors. Lyon, France: IARC Press; 2003:37-41 [33].

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