MYB expression: Potential role in separating adenoid cystic carcinoma (ACC) from pleomorphic adenoma (PA)

Basaloid tumors of the salivary gland both benign and malignant comprise ACC, cellular PA, basal cell adenoma (BCA), and basal cell adenocarcinoma. Rendering a diagnosis given a limited biopsy or fine needle aspiration (FNA) sample proves challenging. Activation of MYB by gene fusion has been found in salivary gland ACCs; therefore we investigated the utility of MYB immunohistochemistry (IHC) as a tool for distinguishing ACCs from other basaloid neoplasms.

We selected 48 cases of ACC (11 FNA blocks [CB]), 37 histologic resections [HR]), 74 PA (36 CB, 38 HR), and 18 BCA (7 CB, 11 HR). FNA CB showed 82% of ACCs (N = 9 of 11) as positive for MYB nuclear staining whereas 68% of ACCs (N = 25 of 37) were positive in HR.

All PA were negative for MYB nuclear staining in both CB (N = 0 of 36) and HR (N = 0 of 38). CB showed 29% of BCA (N = 2 of 7) as positive for MYB nuclear staining and 55% (N = 6 of 11) positive in HR. Both ACC and BCA showed significantly higher mean staining intensity than PA in both CB and HR (P < 0.0001). When comparing ACC and BCA, significantly higher mean staining intensity was observed in CB (P = 0.02382) but not in HR (P = 0.42952).

MYB nuclear staining may prove useful in separating ACC from PA and BCA, especially in limited cellular samples. Diagn. Cytopathol. 2016;44:799-804. © 2016 Wiley Periodicals, Inc.