Metaplastic Breast Carcinoma Hidden Behind a Melanocytic Facade: A Case Report with Literature Review on Metaplastic Breast Carcinoma with Melanocytic Differentiation.

Melanocytic differentiation in breast carcinomas is extremely rare. It often leads to diagnostic dilemmas and should be distinguished from melanoma and pigmented breast lesions, which have significantly different treatment implications and prognoses. The pathogenesis of these tumors is unclear with limited follow-up data. We present one such tumor arising in a female patient in her late 20s, where a final diagnosis of mixed metaplastic carcinoma with melanocytic differentiation and invasive breast carcinoma of no special type was made based on morphological and immunohistochemical evidence. This report discusses the differential diagnosis, insights into the pathogenesis and nomenclature of these tumors, along with a literature review of prior case reports.