Recent developments in salivary gland pathology after the WHO 2024 classification: new developments in existing entities and evolving new entities

Abstract

Parallel to and after publication of the WHO 2024 classification of head and neck tumors, several developments concerning known existing salivary gland tumor entities, but also proposing new evolving tumor entities have been published. This review article describes the most important new developments in salivary gland pathology published through 2022-2025, that were not included in the 5th edition of the WHO Classification of Head and Neck Tumours 2024. This review summarizes these recent developments in both the benign and the malignant tumor categories. Among the recently proposed entities are palisading adenocarcinoma, microcribriform adenocarcinoma, fenestrating adenocarcinoma and skin-analogue poroid carcinoma. Developments in existing carcinoma entities include recognition of mucoacinar carcinoma as subtype of mucoepidermoid carcinoma (MAML2-fused), mucoepidermoid carcinoma without squamous cell differentiation, metatypical adenoid cystic carcinoma, and adenoid cystic carcinoma with prominent tubular hypereosinophilia. In the benign tumor category, recognition of pleomorphic adenoma with canalicular/trabecular phenotype driven by HMGA2 fusions, triphasic basal cell adenoma with S100 protein-positive "stroma", characterized by CTNNB1 mutations, metaplastic Warthin tumor with KRAS mutations and delineation of thymus-like phenotype in non-sebaceous lymphadenoma with recurrent CYLD mutations are the main highlights. Emerging concepts include benign tumor with ductal and papillary morphology (sialadenopapillary ductal tumor). Finally, new grading schemes have been developed/ proposed for acinic cell carcinoma and secretory carcinoma.