Vimentin-positive squamous cell carcinoma arising in a burn scar. A highly malignant neoplasm composed of acantholytic round keratinocytes.

Two patients had unusual squamous cell carcinoma (SCC) arising in a burn scar. The SCCs rapidly recurred and metastasized after radical operation, and the patients died of disseminated metastases. Histopathologically, the SCC was poorly differentiated and consisted of acantholytic round cells that diffusely proliferated into the deep dermis. However, small, solid nests composed of squamoid cells were focally observed. Immunohistochemical studies revealed that the acantholytic round neoplastic cells expressed not only keratin but also vimentin, and the coexpression was substantiated with double immunostaining. Vimentin-positive SCC composed of acantholytic round neoplastic cells may be a highly malignant subset of cutaneous SCC.