Oncocytoid Salivary Tumors: Differential Diagnosis and Utility of Newly Described Immunohistochemistry.

Background: Oncocytoid salivary tumors include several entities such as oncocytoma, Warthin tumor, secretory carcinoma (SC), salivary duct carcinoma (SDC), acinic cell carcinoma (AciCC), oncocytic mucoepidermoid carcinoma (OMEC), intraductal carcinoma, and epithelial myoepithelial carcinoma (EMC). This review investigates the differential diagnosis of oncocytoid salivary tumors and explore the role of newly described immunostains as valuable tools for their diagnosing and potentially guiding treatment options.

Methods: We assess the utility of incorporating new immunohistochemical markers in routine practice to aid in diagnosing oncocytoid salivary tumors and potentially provide treatment options.

Results: In SDC, AR and Her2 immunostains are utilized as diagnostic tools and biomarkers for selecting patients who might benefit from Androgen-deprivation therapy (ADT) and HER2-targeted therapy. Furthermore, nuclear Pan-Trk immunostaining can aid in diagnosing SC. Additionally, NR4A3 immunostaining has been shown high sensitivity and specificity in identifying AciCC in both surgical and cytologic specimens. Similarly, RAS Q61R mutant-specific immunostaining, detected in EMC, may offer a cost-effective diagnostic marker for this tumor. Although further studies are required to evaluate the role of BSND, this marker has been reported to be positive in Warthin tumor and oncocytoma, aiding in differentiating them from other oncocytoid tumors, particularly OMEC. In addition, BRAFV600E mutant-specific immunostaining can serve as a diagnostic and potentially therapeutic marker for oncocytic intraductal carcinoma in mutation positive cases.

Conclusion: Oncocytoid salivary tumors may have overlapping morphologies, posing diagnostic challenges for pathologists. Recently described immunohistochemical markers may offer valuable tools for diagnosing and potentially guiding treatment options for these tumors.