Mammary carcinoma with prominent cytoplasmic lipofuscin granules mimicking melanocytic differentiation

We report a case of mammary carcinoma with striking cytoplasmic pigmentation in a 60-year-old Japanese woman who presented with a self-evident nodular lesion in the left breast. METHODS AND RESULTS: After a fine needle aspiration revealing atypical clusters of cells, an excisional biopsy was performed. Histologically, a partially cystic 18 mm lesion containing a 5-mm mural nodule was present. The mural nodule and adjacent thickened epithelium were comprised of atypical cells focally invading into the cyst wall. Striking abundant granular brown pigment resembling melanin was present in some of the neoplastic cells. The differential diagnosis included metastatic melanoma and mammary carcinoma with melanocytic differentiation. After a series of special stains and immunohistochemical studies, the diagnosis of mammary carcinoma with extensive cytoplasmic lipofuscin pigment was rendered. CONCLUSION: Mammary carcinoma with lipofuscin pigment to the degree seen in this case which mimics melanocytic differentiation has not, to our knowledge, previously been documented.