WHO update Salivary Glands

Introduction

  • Salivary glands exhibit a diversity of neoplasms, prompting the need for updated classifications.

  • The 5th edition of the WHO Classification includes several new tumor entities.

New Tumor Entities in Salivary Gland Classification

  • New Benign Neoplasms:

    • Sclerosing Polycystic Adenoma: Initially classified as a non-neoplastic lesion, now reclassified as a benign neoplasm due to its sclerosing nature.

    • Keratocystoma: Characterized by multicystic spaces lined by stratified squamous epithelium.

    • Intercalated Duct Adenoma: A benign proliferation mirroring normal intercalated ducts.

    • Striated Duct Adenoma: A rare benign tumor resembling normal striated ducts.

  • New Malignant Neoplasms:

    • Microsecretory Adenocarcinoma: A newly identified adenocarcinoma characterized by distinct morphology and MEF2C::SS18 fusion.

    • Sclerosing Microcystic Adenocarcinoma: Resembling cutaneous microcystic adnexal carcinoma, characterized by small infiltrative cords within thick stroma.

Reclassification of Existing Tumors

  • Cribriform Adenocarcinoma of Salivary Gland Origin (CASG): Represents a subtype of Polymorphous Adenocarcinoma (PAC) with ongoing debates about its classification.

  • Mucinous Adenocarcinoma: Now subdivided into distinct subtypes with recurrent AKT1 E17K mutations, suggesting histological diversity within a single entity.

  • Intraductal Carcinoma: Renamed from low-grade salivary duct carcinoma; features papillary and cribriform growth patterns and associated RET gene rearrangements.

Molecular Pathology Insights

  • The latest classifications reflect the increasing significance of molecular testing in diagnosing salivary gland tumors.

  • Genetic Alterations:

    • Gene fusions have shown specific tumor-type associations, enhancing diagnostic accuracy.

    • Molecular changes are integrated into definitions, especially for mucoepidermoid carcinoma and adenoid cystic carcinoma.

Diagnostic Advances

  • Cytological findings, particularly through FNA, recognized for their importance in initial diagnostics, with recommendations for the Milan system.

  • Core biopsies, though providing more architectural information, remain less efficacious in distinguishing between benign and malignant tumors.

  • Histologic grading serves as a predictor of clinical behavior, although universal grading schemes are not universally applicable.

Structural Insights and Morphology

  • Sclerosing Polycystic Adenoma (SPA): Characterized by fibrosis and duct alterations with links to apocrine intraductal carcinoma.

  • Keratocystoma: Identified by its cystic nature with well-defined solid squamous islands.

  • Intercalated Duct Adenoma (IDA): Displays bilateral duct proliferation with subtle cytological features indicative of normal intercalated ducts.

  • Striated Duct Adenoma: Features closely apposed ducts without myoepithelial cells, relying on immunoprofiles distinct from other types.

Emerging and Controversial Issues

  • The relationship between mucinous adenocarcinoma, intraductal papillary mucinous neoplasm (IPMN), and potential precursor relations still under investigation.

  • Oncocytic Neoplasms: Lack of consensus regarding the classification of purely oncocytic carcinomas; many tumors are currently categorized as oncocytic variants of other carcinomas.

Conclusion

  • Recent advances in molecular pathology have significantly enhanced the classification and understanding of salivary tumors.

  • Continued research will likely lead to further refinement of tumor categories based on established genetic alterations.