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) 

In This Article

Pigmented Squamous Cell Carcinoma

Only a few reports of infiltrating pigmented SCC of the skin(IPSCC) are available. A report by Jurado and colleagues[36] in 1998 describes two cases of IPSCC. Both occurred in elderly men and were located on the face. In one case,the tumor had been slowly growing over a period of several years,and clinically it resembled a melanoma. The other case resembled a pigmented basal cell carcinoma(BCC). Both tumors were excised, with no evidence of recurrence or metastasis after a 4-year follow-up. A more recent report by Morgan et al[37] evaluated five cases of IPSCC. These tumors all presented as rapidly growing crusted papules on actinic damaged skin of the face. After excision, an average follow-up of 4 years failed to demonstrate any local recurrence or metastasis.

The histology of these tumors demonstrates a mixture of keratinized squamous cells and melanin-producing dendritic melanocytes.The squamous cells stain positively with epithelial membrane antigen and and both low- and high-molecular keratin. Melanin can be confirmed with a Fontana-Masson stain. The dendritic cells are reactive with vimentin, S100 protein,and HMB45. Some of the neoplastic squamous cells have been reported to demonstrate focal positivity for S100 and HMB45, which may be due to transference of antigen from the dendritic melanocytes to the neoplastic cells.

The differential diagnosis of IPSCC includes pigmented BCC,pilomatrixoma, dermal squamomelanocytic tumor, and melanoma with pseudoepitheliomatous hyperplasia.[37] Pigmented BCC can be distinguished by the presence of peripherally palisading basaloid cells, limited keratinization, and negative staining for epithelial membrane antigen and high-molecular-weight keratins. pilomatrixomahas characteristic "ghost cells"and also stains negatively for epithelial membrane antigen and high molecular-weight keratins. Melanoma with pseudoepitheliomatous hyperplasia has benign-appearing epithelial cells with atypical-appearing melanocytes,which contrasts to the atypical squamous cells with banal-appearing melanocytes in IPSCC. The dermal squamo-melanocytic tumor can be distinguished by the presence of nonkeratinizinga typical nonpigmented cells that are negative for both S100 and keratin antibodies.[37]

Due to the small number of reported cases, it is difficult to make any definitive conclusions regarding the malignant potential of IPSCC.

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