Basal cell carcinoma with myoepithelial differentiation.

A lesion from the left cheek of a 48-year-old man showed a neoplasm composed primarily of cells with eccentric crescent-shaped nuclei and abundant, homogenous, eosinophilic cytoplasm resembling signet ring cells. Immunohistochemical studies showed the cells to stain positively for pan cytokeratin and smooth muscle actin, indicating myoepithelial differentiation (MED). Foci of conventional basal cell carcinoma were present, and cells with MED were also admixed within some of the aggregations of basal cell carcinoma. On the basis of these findings, we interpreted this lesion to represent basal cell carcinoma with MED. A review of the existing literature of basal cell carcinomas with similar morphologic features is also presented.