Primary and metastatic epidermotropic pigmented breast carcinoma: histological, immunohistochemical and ultrastructural analysis of four cases

The appearance of breast carcinoma as a pigmented lesion, primitive or metastatic, is an exceedingly rare event. The histomorphological, immunohistochemical and ultrastructural aspects of this pattern, seem to be the result of a mechanism developing each time the neoplastic cells with epidermotropic properties surpass the dermo-epidermal junction. We report 4 cases of pigmented skin lesions, apparently primitive in one case, secondary in 3 cases, of breast carcinoma, clinically mimicking malignant melanoma. Histomorphology and immunohistochemical analysis with the Alkaline-Phosphatase anti-Alkaline-Phosphatase (APAAP) method, using the following mono- and polyclonal antibodies: S100 protein, HMB45, epithelial membrane antigen (EMA), Cytokeratin A, estrogen and progestagen receptors, ki67, PCNA, were performed. Retrospective ultrastructural investigation was performed by reprocessing the paraffin embedded material. Neoplasm was found positive for both epithelial and melanocyte markers and a histomorphological pattern indicative for malignant melanoma was observed. Ultrastructurally, neoplastic cells were seen to contain melanin pigment but at the same time presented characteristics of epithelial glandular cells. Our data suggest that breast carcinoma sometime shows a polyvalent phenotype and the neoplastic elements are moreover capable of acquiring antigenic characteristics typical of the melanocyte. This peculiar behavior must be kept in mind for the correct diagnosis, especially when the pigmented skin lesions are the first manifestation of the tumor.