Salivary gland carcinomas have clinically been divided into three groups in terms of prognosis: low-, intermediate-, and high-grade1. Histologic grade is determined by the pathologist on a case-by-case basis after comprehensive consideration of the microscopical findings1. However, certain tumor types may denote specific grade, while others include various degrees of malignancy, and histologic grading systems have been proposed in some tumors1,2.

Histologic grade represents one of the primarily indicators of salivary gland carcinoma prognosis3,4. High-grade carcinomas are characterized by poor prognosis associated with highly malignant histologic features, such as nuclear pleomorphism, vascular invasion, perineural invasion, necrosis, brisk mitosis, and are often treated more intensively than low- or intermediate-grade carcinomas5, 6, 7. Therefore, even if the precise tumor type cannot be determined by fine-needle aspiration biopsy, core needle biopsy, or frozen section, the diagnosis of high-grade carcinoma has a clinical impact on the decision-making treatment strategy. However, with recent advances in molecular techniques8, it has facilitated to appropriately classify cases that were previously diagnosed as “adenocarcinoma, NOS” into specific tumor types9. Furthermore, as with the development of molecular-targeted therapy, it has been evident that several carcinomas are highly linked with personalized treatment 10,11, the identification of pathologic tumor type becomes more important than previous.

In this article, we cover the updated clinicopathological features of the representative high-grade salivary gland carcinomas: salivary duct carcinoma (SDC) and its histological subtypes, high-grade mucoepidermoid carcinoma (MEC), solid-type adenoid cystic carcinoma (AdCC), and high-grade transformation (HGT) of low- or intermediate-grade salivary gland carcinoma, including the differential diagnosis, which are helpful in the practical settings.