Abstract

Cutaneous malignant squamomelanocytic tumor (SMT) is a rare neoplasm comprised of two distinct cell populations of squamous cell carcinoma (SCC) and a melanocytic component. Despite increasing literature reports, the origin and pathophysiology is poorly understood. Discussed are two cases of SMT with dendritic melanocytes and centered around a hair follicle. First is an 75-year-old male who presented with a 1 cm blue nodule on the shoulder. Histopathology revealed malignant proliferation of epithelioid cells with easily identified mitoses and pigmented dendritic cells in a nodular pattern. H&E sections showed the tumor arising from the edge of a pilosebaceous unit near the bulge/germinative area. There was no intraepidermal component. The epithelioid appearing cells marked with p40 and CK5/6 on immunohistochemistry (IHC), while the dendritic cells at the periphery of the lesion were positive for melanocytic markers. Second is an 82-year-old female who presented with an ulcerated nodule on the neck. Biopsy revealed an ulcerated malignant neoplasm with similar histopathology to the first case, also associated with pilosebaceous units and one area was suspicious for origin from a hair follicle largely replaced by the tumor. As both epidermal melanocytes and keratinocytes arise from the bulge area of hair follicles, we suspect that the etiology of the SMT could be from germinative cells in the hair bulb region of pilosebaceous units. The first presented case shows a SMT arising just off the wall of a pilosebaceous near the bulge area and the second shows areas suggestive of a SMT replacing a hair follicle unit.