Eccrine porocarcinoma: a case with an obscure primary tumor diagnosed from lymph node metastasis.

Eccrine porocarcinoma (EPC), a rare malignant epidermal appendage tumor, is mainly seen in elderly patients. A long history is one of its main characteristics. Two types of EPC are known: juxtaepidermal and dermal. The juxtaepidermal type usually has a more aggressive behavior. Lymph node metastasis and high mitotic activity are associated with poor prognosis. A case of EPC with a long-standing but indolent primary site diagnosed from lymph node metastasis is presented here. There was also accompanying chronic dermatitis as a paraneoplastic syndrome. Diagnosing EPC prior to the regional lymph node involvement is the most valuable factor for a successful treatment. Persistent examinations and attempts to find the primary site(s) have to be made in such cases.