Fine-needle aspiration (FNA) biopsy of salivary gland neoplasms can have a variety of overlapping appearances. Basaloid neoplasms can be a diagnostic challenge, and FNA cytomorphology alone cannot always provide a definitive diagnosis.
To examine the incidence and potential utility of detecting a MYB translocation by fluorescence in situ hybridization (FISH) in adenoid cystic carcinomas (AdCCs) and pleomorphic adenoma FNA smears with known surgical outcomes.
Patients who underwent FNA biopsy for surgically confirmed AdCCs and pleomorphic adenomas were identified. Fluorescence in situ hybridization, using commercially available fluorescent-labeled probes, hybridizing to MYB-telomeric and MYB-centromeric, was used to identify the MYB gene and to evaluate it for abnormalities and translocation. Using a fluorescent microscope, 4',6-diamidino-2-phenylindole (DAPI)-stained, nonoverlapping cells were counted, and 10% or greater abnormal cells were considered positive.
The 10 AdCC and 13 pleomorphic adenoma FNA cases had FISH evaluations performed; 50% (5 of 10) of the AdCC cases showed a MYB abnormality by FISH; 40% (4 of 10) AdCCs showed a positive break-apart signal in most cells (48%-84%). One case (10%) of AdCC showed a trisomy MYB signal pattern without the break-apart translocation pattern. Of the 13 pleomorphic adenomas, none (0%) of the cases showed a MYB translocation or abnormality by FISH. MYB FISH abnormalities showed a 100% positive predictive value, 50% sensitivity, and 100% specificity, when differentiating AdCC from pleomorphic adenoma.
MYB gene abnormalities were present in 50% (5 of 10) of the AdCC cases. This corresponds to the reported prevalence in formalin-fixed, paraffin-embedded tissue for AdCC surgical resections. Using FISH testing for detecting MYB gene abnormalities in the salivary gland of FNA biopsies has the potential to provide additional, helpful ancillary information in diagnosing AdCC.