Utility of NR4A3 on FNA cytology smears and liquid‐based preparations of salivary gland

Background Fine‐needle aspiration cytology (FNAC) is generally the initial sampling method for salivary gland neoplasms. The cytomorphologic features of acinic cell carcinoma (AciCC) of salivary gland can overlap with other neoplastic and nonneoplastic entities. AciCCs harbor a recurrent t(4;9) rearrangement with upregulation of nuclear receptor subfamily 4 group A member 3 (NR4A3). NR4A3 protein overexpression has been shown to be highly sensitive and specific for the diagnosis of AciCC in histologic specimens and cell block preparations. However, data on NR4A3 immunocytochemistry (ICC) on conventional smears or liquid‐based cytology are limited. Methods The authors identified 18 FNAC of histologically proven AciCC cases between 2013 and 2019. FNAC samples of diagnostic mimickers were likewise retrieved and included in the study cohort for comparison. The NOR1/NR4A3 mouse monoclonal antibody was applied directly to FNAC slides using a standard ICC technique. Results The cohort included ethanol‐fixed Papanicolaou‐stained cytologic smears and liquid‐based preparations from 18 AciCC, one secretory carcinoma, four mucoepidermoid carcinomas, four salivary duct carcinomas, five pleomorphic adenomas (PA), five Warthin tumors, five oncocytomas, one oncocytic hyperplasia, and five nonneoplastic salivary gland cases. Strong nuclear staining for NR4A3 was present in all AciCC, weak nuclear staining was present in one PA, and all other non‐AciCC were negative (sensitivity, 100%; specificity, 97%). Conclusions NR4A3 ICC can be used directly on FNAC conventional smears and liquid‐based cytology to reliably distinguish AciCC from its mimickers. This marker may be useful in cases where a cell block preparation is unavailable or inadequate. NR4A3 immunocytochemistry can be used directly on fine‐needle aspiration cytology conventional smears and liquid‐based cytology to reliably distinguish acinic cell carcinoma from its mimickers. This may be useful in cases where a cell block preparation is unavailable or inadequate.