Fine-needle aspiration of a metaplastic breast carcinoma with extensive melanocytic differentiation: a case report.

Metaplastic carcinomas of the breast are uncommon breast tumors with aberrant cellular differentiation, most commonly showing ductal, squamous, and mesenchymal components. A breast carcinoma composed of both epithelial and melanocytic differentiation is rare, with only four previously reported cases in the literature. We present the fifth reported case, where the diagnosis was suggested by fine-needle aspiration (FNA) and later confirmed after the surgical specimen was excised. Histologically, this neoplasm revealed multidirectional differentiation, consisting primarily of squamous and melanocytic cell types, with focal glandular and osseous metaplasia. Based on the morphologic, immunohistochemical, and ultrastructural findings, we conclude that such tumors fall within the spectrum of metaplastic carcinomas of the breast. We believe that this case will further contribute to the understanding of this enigmatic tumor.