Undifferentiated carcinomas of salivary glands. Undifferentiated carcinomas of salivary glands are those epithelial malignancies whose light-optic histopathologic features are not sufficient to place them in other defined classes of carcinoma. They are ultrastructurally heterogeneous and can manifest neuroendocrine differentiation. With or without the latter, the carcinomas are biologically high-grade and rank with salivary duct and high-grade mucoepidermoid carcinomas in terms of morbidity and mortality. 