NOR-1 distinguishes acinic cell carcinoma from its mimics on fine-needle aspiration biopsy specimens

Acinic cell carcinoma of the salivary gland (ACC-SG) is characterized by a recurrent chromosomal rearrangement (t(4; 9)(q13; q31)) that upregulates the transcription factor NR4A3. Studies conducted on formalin-fixed paraffin-embedded (FFPE) tissue have found that nuclear expression of a monoclonal antibody NR4A3 (NOR-1) is a sensitive and specific diagnostic marker for ACC-SG. The aims of this study were to evaluate the performance of the NOR-1 antibody and to compare its utility in separating ACC-SG from its mimics on cytology cell block specimens. Cell blocks were obtained from 70 fine-needle aspiration specimens from multiple institutional archives over a 7-year period (2013-2019). These included 10 cases of conventional low-grade ACC-SG, 1 case of dedifferentiated high-grade ACC-SG, and 59 cases of non-ACC-SG. An automated immunohistochemistry system (Bond-III, Leica) was used for the detection of NR4A3, using the commercially available antibody NOR-1 (sc-393902 [H-7], Santa Cruz Biotechnology Inc.). Optimization of the antibody on the cell blocks was successfully completed by increasing the titer from 1:100 (suggested titer for FFPE specimens) to 1:30. Distinct nuclear reactivity was observed in all 11 cases of ACC-SG (10 of 11 with 3+ diffuse nuclear positivity and 1 case with 2+ focal reactivity). Expression of NR4A3 was absent in all non-ACC-SG cases in the cell blocks. Application of the NOR-1 immunohistochemical staining in fine-needle aspirates of salivary gland tumors for which ACC-SG is a diagnostic consideration successfully distinguishes ACC-SG from its cytologic mimics and provides an early opportunity for oncologic intervention.