The Utility of BSND Immunohistochemistry in the Differential Diagnosis of Oncocytic and Warthin-like Mucoepidermoid Carcinoma of Salivary Gland.

Purpose: BSND is a chloride channel subunit that is expressed in the normal salivary gland. We aimed to validate the utility of BSND immunohistochemistry in the differential diagnosis of oncocytic salivary gland neoplasms.

Methods: BSND immunohistochemistry was performed in a retrospective cohort of 93 salivary gland lesions, enriched with tumors with oncocytic features and histologic variants of mucoepidermoid carcinoma (MEC).

Results: All oncocytomas (n = 18) showed diffuse membranous BSND immunopositivity. Warthin tumors (n = 18) were also positive for BSND, but the staining pattern was patchy cytoplasmic and membranous in 10-25% of tumor cells. Using a threshold of 10% BSND-positive cells, all Warthin tumors were positive, while none of Warthin-like MECs or non-MEC salivary tumors were positive. Applying the same 10% positivity criterion, two oncocytic MECs were positive for BSND. The percentage of BSND staining in oncocytic MECs was up to 20%. In contrast, BSND was diffusely positive in oncocytomas with a median percentage of positivity of 95% (range: 40 - 100%). Therefore, a higher threshold of > 20% BSND-positive cells may be considered when differentiating between oncocytoma and oncocytic MEC.

Conclusion: BSND immunohistochemistry is a potentially useful diagnostic marker for salivary gland neoplasms, especially oncocytic and Warthin-like MECs. A threshold of ≥ 10% positivity can differentiate Warthin tumors from Warthin-like MECs, whereas > 20% positivity can be effective for separating oncocytomas from oncocytic MECs.