The Utility of MYB Immunohistochemistry (IHC) in Fine Needle Aspiration (FNA) Diagnosis of Adenoid Cystic Carcinoma (AdCC).

Differentiating adenoid cystic carcinoma (AdCC) from other basaloid neoplasm in a fine needle aspiration (FNA) sample can be challenging. Activation of MYB in AdCC by the fusion transcript MYB-NFIB has been recently demonstrated in salivary gland and other organs. The aim of this study is to evaluate the utility of MYB immunohistochemistry (IHC) in distinguishing AdCCs and other basaloid neoplasm in cytology specimens. Eighteen FNA cases, from salivary gland and other sites, and their subsequent surgical resection specimens were included in the study. Eight cases were confirmed AdCC on resection. MYB IHC was performed on slides made from cytology cell block and surgical resection paraffin blocks. Percentage and intensity of nuclear staining in tumor cells was scored as 0 to 3. The staining results were concordant between cytology specimens and their corresponding surgical resection tumors. Strong diffuse nuclear staining (score 3, N = 5) was exclusively observed in AdCC, both in cytology and surgical specimens. Only one pleomorphic adenoma and one poorly differentiated basaloid carcinoma were positive for MYB staining (score 1 to 2). Any degree of nuclear MYB labeling was seen in 100% AdCC cases (N = 8/8) compared with of 20% (N = 2/10) of all other non-AdCC cases (P = < 0.001). The sensitivity and specificity of any degree MYB positivity for AdCC in cytology specimen is 100% and 78%. The sensitivity and specificity of strong diffuse MYB labeling (score 2 to 3) for AdCC is 83% and 100% in cytology specimen. Strong diffuse nuclear staining of MYB is valuable in supporting a cytologic diagnosis of AdCC. However, weak and focal labeling of MYB should be interpreted with caution as it can be seen in benign and other malignant basaloid lesions.