Biphasic Sarcomatoid Porocarcinoma.

Sarcomatoid carcinomas are rare malignant tumors, which usually demonstrate a well-differentiated epithelial component in association with a poorly differentiated spindle-cell component. Several different subtypes have been reported and categorized primarily under the differentiated epithelial component, with the majority of cutaneous sarcomatoid carcinomas arising in the setting of a basal cell or squamous cell carcinoma. To date, only 4 cases of sarcomatoid porocarcinoma have been reported in the literature. The authors present a case of an 84-year-old woman with an ulcerated papule on her scalp for several months. Histopathology revealed an exophytic and endophytic epidermal proliferation with multiple mitoses and ductal differentiation overlying a poorly differentiated, infiltrative spindle-cell proliferation in the dermis. Ductal and cystic structures were scattered throughout the malignancy. Immunohistochemistry was notable for strong and diffuse pancytokeratin positivity, p63 positivity, focally positive carcinoembryonic antigen within the ductal lumina, and periodic acid-schiff-positive, diastase-resistant intracellular deposits. They present the findings of this rare case of primary cutaneous sarcomatoid porocarcinoma.