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Monophasic sarcomatoid eccrine porocarcinoma. Report of a case and literature review.

Sarcomatoid porocarcinoma (SP) is a rare subtype of porocarcinoma composed of both malignant epithelial and sarcoma-like components. To our knowledge, only eight cases of this neoplasm have been published, all of them biphasic. A 42-year-old man presented with a latero-cervical nodule that had been noted for about five months. Histopathological study revealed an infiltrative tumor within the dermis and hypodermis without connection to epidermis, whose diagnosis was monophasic sarcomatoid eccrine porocarcinoma (SEP). The study of nine cases de SP, including the present, revealed that the ages of the patients ranged from 42 to 89 years (mean 72.3 years). There was no clear difference in the incidence with respect to gender. The location of the tumor was most common in the head and neck, followed by lower extremity. The size ranged from 2.5 cm to 3.5 cm (mean 3 cm). At the time of diagnosis, six (66.7%) lesions were ulcerated. No case was clinically diagnosed. Residual poroma was present in six (66.7%) cases. Only one case showed apocrine differentiation. Mitoses and comedonecrosis were frequent. Of the cases published, only four had a follow-up of at least 16 months. One patient succumbed to the tumor. We report for the first time a case of monophasic SEP without epidermal connection. The patient presented a regional lymph node metastasis three months after excision. The main differential diagnosis includes primary dermal melanoma and other rare variants of cutaneous melanoma, primary cutaneous clear cell sarcoma, primary cutaneous synovial sarcoma, and cutaneous metastasis from visceral sarcomatoid carcinoma.