Transepidermal elimination of tumor cells in a metastatic breast carcinoma- A rare case with an usual presentation

Summary: Non cutaneous malignancy metastasis to the skin occur with different locations having different propensity for certain types of malignancy. Of these malignancies metastatic breast carcinoma is most common. There are several malignancies known to have epidermotropic metastasis such as breast carcinoma, colonic adenocarcinoma, and melanoma among others. However, it is uncommon to see transepidermal elimination. We present a case of a 65-year-old woman with a history of metastatic breast carcinoma with a right post auricular nodule. The clinical differential included an epidermal inclusion cyst versus metastasis. The excisional biopsy showed both a nodular and infiltrative process of atypical epithelioid cells with areas of glandular formation. Along the dermal-epidermal junction were foci of epidermotropic tumor cells with some areas showcasing transepidermal elimination of tumor cells. The lesional cells were positive for TRPS-1, GATA 3, and CK7. Lesional cells were negative for P40, CK20, and TTF-1. This case highlights a rare finding of transepidermal elimination of tumor cells in a metastatic breast carcinoma.