Histologic Considerations and Salivary Gland Tumor Classification in Surgical Pathology

The classification of salivary gland neoplasms is dynamic and continues to evolve as reflected in the 2022 fifth edition World Health Organization (WHO) Classification of Head and Neck Tumours. A significant contributor to the evolution in the classification of salivary gland tumors is the utilization of molecular testing in their diagnosis and differential diagnosis. Since the fourth edition of the WHO Classification more salivary gland tumors have been shown to harbor tumor type-specific rearrangements resulting in the identification of new types of salivary gland tumors or a delineation of specific subtypes within previously established tumor types. In addition to the tumor types with previously defining molecular alterations including pleomorphic adenoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, secretory carcinoma, hyalinizing clear cell carcinoma, epithelial-myoepithelial carcinoma, and myoepithelial carcinoma, more recently molecularly defined tumor types include intraductal carcinoma, microsecretory carcinoma, and mucinous adenocarcinoma. Undoubtedly, molecular testing has significantly contributed to the advances in the diagnosis of salivary gland tumors but the basis in the evaluation of all salivary gland lesions remains their histology supported by immunohistochemical features. This fact is reflected in the WHO classification which is a morphologic-based classification separating neoplastic entities primarily on tumor morphology to predict their biological behavior, albeit buttressed by immunohistochemical staining and molecular testing.