Follicular squamous cell carcinoma of the skin: a poorly recognized neoplasm arising from the wall of hair follicles.

Abstract

In the last decades, a number of clinicopathologic subtypes of squamous cell carcinoma (SCC) of the skin, ranging from highly aggressive tumors with a tendency to recur and metastasize to neoplasms with a favorable prognosis, have been described. SCCs arising from the wall of hair follicles have been briefly mentioned by some authors but never reported in a series. Cases of SCC arising from the wall of hair follicles were collected from the files of two large German Centers for Dermatopathology and analyzed clinicopathologically and immunohistochemically. Sixteen cases of SCC developing in hair follicles were found among more than 7000 cases of cutaneous SCC reviewed. In most cases, tumors arose on sun-damaged skin of the face of elderly persons. There was a male predominance (11/5). The most common clinical diagnosis was basal cell carcinoma (BCC). Microscopically, tumors developed in the upper part of hair follicles without or with focal involvement of the overlying epidermis at the border with the involved follicle. Immunohistochemically, tumors were positive for cytokeratin and negative for a battery of immunomarkers, including antibodies against the most common carcinogenic human papillomaviruses (HPV) of the skin. Most tumors were excised by simple excision. In two cases, a recurrence was noted after incomplete excision. No further recurrences or metastasis have been noted after a follow-up period ranging from 11 months to 12 years. SCC of the hair follicle represents a poorly recognized but distinctive subset of SCC of the skin that should be considered in the differential diagnosis of other cutaneous epithelial tumors. The term follicular SCC (FSCC) is proposed for this neoplasm.