Fluorescence in situ hybridization for ETV6 gene rearrangements on destained cytological smears: Role in diagnosis of secretory carcinoma of salivary gland

Background Fine-needle aspiration cytology (FNAC) is the first-line diagnostic procedure for salivary gland masses. Secretory carcinoma (SC) is characterized by ETV6 and RET rearrangements detected by fluorescence in situ hybridization (FISH) or reverse transcriptase-polymerase chain reaction optimized for paraffin-embedded and fresh-frozen tissue, respectively. The authors performed FISH on cytological material to assess its role in the diagnosis of SC. Methods FNACs with SC as a diagnostic consideration and cases diagnosed as SC on histology with a corresponding FNAC with any diagnosis were evaluated for ETV6 rearrangement by FISH. If acinic cell carcinoma (ACC) was a differential diagnosis and ETV6 rearrangement was absent, NR4A3 FISH was performed. FISH results were compared with those on histological specimens, where available. Results Fifteen cases were included. FISH initially performed on three cell blocks did not yield good results, was then performed on direct smears, and was interpretable in 14 cases (93.3%). An ETV6 rearrangement was identified in seven cases (50%), and an NR4A3 rearrangement was identified in three cases (21.4%), providing a confirmatory diagnosis in 10 of 15 cases (66.7%). The Milan System for Reporting Salivary Gland Cytopathology category was altered in two cases (6.7%). Complete correlation (100%) was seen with FISH on corresponding histological specimens. Conclusions With minor modifications, the FISH procedure can be optimized for FNAC smears with results comparable to those on histological specimens. ETV6 FISH testing on cytological smears in cases suspected as SC improves the diagnostic accuracy of FNAC and can help lower the proportion of the Milan categories salivary gland neoplasm of uncertain malignant potential and suspicious for malignancy, maximizing diagnostic information from less invasive samples and aiding in patient management.