[Unusual axillary apocrine carcinoma of the skin: histological diagnostic difficulties]

Apocrine carcinoma of the skin (ACS) is a rare adnexal neoplasm presenting as an indurated slow-growing dermal or subcutaneous plaque that often occurs in the axilla. Histological distinction between ACS and cutaneous metastases of breast carcinoma may be difficult.

A 64-year-old man presented with a slowly growing left axillary mass, which he had noticed for 2 years, without any other functional or clinical symptoms. Histological examination of the skin biopsy showed dermal invasion with atypical cells in an "Indian file" pattern. The pattern of the tumour and immunohistochemical staining suggested a diagnosis of breast carcinoma metastasis. However, the history of a slow-growing tumour and negative initial testing for a primary adenocarcinoma supported the hypothesis of ACS.

A 100 cases of ACS have been reported in the literature with the main site being the axillary area. The differential diagnostic between axillary ACS and metastasis of lobular breast carcinoma has been discussed recently. Diagnosis may be difficult since the pattern of the tumour can be misleading and immunomarkers are not always specific.

We report a new case of axillary ACS histologically mimicking lobular breast carcinoma metastasis.