Background. Squamous cell carcinomas (SCCs) of the skin have a wide range of histologic subtypes and there are indications of differences in prognosis.

Objective. The morphologic variety of SCCs with respect to its biological behavior and the further course of disease is analyzed, with emphasis on histopathologic criteria, briefly quoting the main clinical and pathogenetic aspects.

Methods. Referring to the international tumor classification of the World Health Organization, histologically different carcinoma variants are presented and discussed, based on a review of the literature regarding each subtype, and also including the desmoplastic SCC type.

Results. Histologically, common invasive SCCs are most frequently found, while metastases mainly occur in tumors of high thickness and poor differentiation. The immature spindle cell carcinoma type resembles sarcoma and may grow rapidly with an aggressive clinical course. Lymphoepithelioma-like carcinoma of the skin is extremely rare and its histogenesis remains to be elucidated. Thus far, one case with metastasis and lethal outcome has been reported. As details determining the progression ability have so far only been scanty and partially contradictory, more investigations are necessary, especially for acantholytic SCCs and invasive SCCs developing from Bowen's disease, whereas verrucous carcinomas can be categorized as low malignancy neoplasms. Desmoplastic SCCs, especially with large tumor thickness, should be separated from other SCC subtypes due to their high risk of local recurrence and metastatic spread.

Conclusion. The future outcome of SCCs of the skin is significantly influenced by their histologic grade and tumor thickness. In addition, subtyping represents another valuable histopathologic tool for improving the assessment of malignancy.