Pigmented primary carcinoma of the breast: a clinical mimic of malignant melanoma.

A 68-year-old man had a pigmented tumour in the breast. Although the clinical picture suggested a malignant melanoma, histology revealed that the tumour was a primary ductal carcinoma of the breast. There was no pagetoid cell proliferation in the epidermis. However, tumour nests contained numerous dendritic melanocytes that could survive in the tumour nests without the existence of epidermal keratinocytes. Further immunohistochemical study employing antibodies to melanocyte growth factors demonstrated that anti-basic fibroblast growth factor (bFGF) antibody was the only reagent to show a positive staining for tumour cells. This indicated that the breast cancer cells produced bFGF, which enabled survival of melanocytes within the tumour mass.