An immunohistochemical study of a carcinoma of the parotid gland exhibiting both ductal and acinic cell differentiation.

A 76-year-old man underwent a subtotal parotidectomy for removal of a 3 cm. multicystic mass. The tumor was a salivary gland carcinoma, with both infiltrating and intraductal/intra-acinar components, exhibiting three histologic patterns: cribriform, papillary, and comedo-like. Immunohistochemical stain for keratin by the immunoperoxidase technique was strongly reactive in the vast majority of the tumor cells, indicating ductal differentiation of the tumor. Ultrastructural studies indicated primarily ductal differentiation of the tumor cells, with additional areas of acinous and myoepithelial differentiation.