Apocrine carcinoma with signet ring cells and histiocytoid features. A potentially confusing axillary tumor.

A case of carcinoma of the axillary apocrine gland in a 42-year-old man is reported. The cytomorphic features of this tumor on fine-needle aspiration closely resemble invasive lobular carcinoma of the breast. Both in situ, and invasive apocrine gland carcinoma were present within the excision specimen, and metastatic tumor was found in the axillary lymph nodes. On histologic, immunohistochemical and ultrastructural examination, the tumor was similar to invasive lobular carcinoma of the breast. The tumor cells analyzed by cytometry displayed a diploid pattern. Serial sections of the whole resected specimen failed to reveal breast parenchyma. To the best of our knowledge, this is the first case presented in axilla of an unusual variant of carcinoma of the skin, very similar or identical to six other cases located on the eyelids. The descriptive term "apocrine carcinoma with signet ring cells and histiocytoid features" is proposed in order to emphasize that these tumors are easily confused with benign conditions, mammary cancer and other metastatic carcinomas.