Syringoid Eccrine Carcinoma of the Foot: Report of a Rare Cutaneous Adnexal Neoplasm.

Syringoid eccrine carcinoma is a rare malignant adnexal tumor that typically presents in the head and neck region. Involvement of the extremities is uncommon, with only a few cases reported in the literature. Here, we report our experience with a rare case of syringoid eccrine carcinoma occurring on the plantar surface of the right foot in a 47-year-old African American woman. Histologically, incisional biopsy revealed a tumor consisting of tubulocystic structures lined by basaloid cells with an infiltrative growth pattern, extending from the reticular dermis to the deep biopsy margin. Some of the nests and cords of basaloid cells displayed syringoma-like, tadpole morphology. Immunohistochemical analysis showed diffuse immunoreactivity with monoclonal carcinoembryonic antigen, epithelial membrane antigen, cytokeratin 7, S100 protein, and CD117. These morphologic and immunophenotypic features were most consistent with syringoid eccrine carcinoma. Syringoid eccrine carcinoma has a broad differential diagnosis which must be carefully ruled out by morphology, immunohistochemistry, and thorough metastatic survey with imaging studies. Our case highlights the importance of recognizing this rare entity, which is locally destructive and has a propensity for recurrence. To the best of our knowledge, this is the first reported case of syringoid eccrine carcinoma presenting on the sole of the foot.