[Eccrine carcinoma: a diagnostic pitfall]

The eccrine carcinoma is a rare form of skin adnexal malignancy, usually presenting as a locally invasive, solitary lesion in the head and neck region. Histopathologically and immunohistochemically, eccrine carcinomas are difficult to differentiate from cutaneous metastases of breast carcinomas. Unlike treatment of cutaneous metastasis, treatment of a solitary eccrine carcinoma entails excision, generally without systematic therapy.

A seventy-year-old woman previously treated definitively for (in situ) breast cancer, undergoes excision of a nodule on the scalp. The histopathology report indicates a lesion typical for cutaneous metastasis of breast carcinoma. However, diagnostic imaging excludes recurrent breast cancer or metastatic spread. When subsequent clonality testing with archived breast cancer tissue from the earlier episode does not show a relation, the pathologist defines the lesion as an eccrine carcinoma. A re-excision is conducted, which does not show any residual tumorous tissue, and at follow-up there are no signs of recurrence or metastases.

As a relatively rare and unknown malignancy, with strong histopathological resemblance to cutaneous metastasis of breast carcinoma, eccrine carcinoma poses a diagnostic challenge to both clinicians and pathologists.