Histologic Variants of Squamous Cell Carcinoma of the Skin

Margaret H. Rinker, MD; Neil A. Fenske, MD; Leigh Ann Scalf, MD, and L. Frank Glass, MD, Division of Dermatology and Cutaneous Surgery, Department of Internal Medicine at the University of South Florida, Tampa, Fla.

Cancer Control. 2001;8(4) 

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Spindle Cell Squamous Cell Carcinoma

Spindle cell SCC is a rare variant of SCC. Clinically, it may appear as an exophytic tumor or an ulcerated mass on the sun-exposed skin of elderly patients. Histologically, it is composed of atypical spindle cells arranged in a whorled pattern. Unlike conventional SCC, the tumor cells infiltrate the dermis singly, without the formation of nests and cords.There may or may not be connection to the overlying epidermis.Mitoses and bizarre pleomorphic giant cells may be frequently seen. Deep infiltration of the dermis,sub cutis, and underlying fascia is common. Spindle cell SCC may be difficult to distinguish from an atypical fibroxanthoma or adesmoplastic melanoma, in which case immunohistochemistry is required. Spindle cell SCC will stain positive for high-molecular weight CK and EMA. Atypical fibroxanthomas will stain positive for vimentin, and spindle cell melanomas will stain positive for S100 protein. Some poorly differentiated spindle cell SCCs may show loss of cytokeratin expression and aberrant vimentin expression,making the diagnosis even more challenging.[15] Electron microscopy can be used in addition to immunohistochemistry to confirm the diagnosis. The presence of tonofilaments and desmosomes confirms an epithelial origin.[16] Poorly differentiated spindle cell SCC, however, may not always have evidence of tonofilaments and desmosomes, making them indistinguishable from sarcomas.

Spindle cell SCC was initially reported by Martin and Stewart in 1935.[17] It was believed that previous radiation was the most important cause, as six of the eight patients reported had a history of radiation. It was also thought to bean aggressive form of SCC, as four of these eight patients died of the cancer. This was disputed in 1950 in a report of five cases by Strauss[18] in which none of the patients had a history of radiation exposure. In the follow-up of these patients,there were no reports of recurrence or metastasis. In 1972, Smith[19] proposed that when spindle cell SCCs arise in a site of previous radiation, they tend to have a more aggressive course, as would be expected. When they arise de novo, Smith proposed that these lesions do not exhibit a more aggressive behavior than conventional SCC. Spindle cell SCC has also been reported in renal transplant patients, in which one of four patients developed metastatic disease.[15] Unfortunately, no large studies have been conducted regarding the prognosis of spindle cell SCC, especially comparing de novo lesions with radiation-associated lesions.

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