Immunohistochemical Expression of TRK and NR4A3 in a Cohort of Salivary Gland Neoplasms

The diagnosis of cancers arising in salivary glands is often challenging due to the fact that different tumor types may show similar characteristic under the microscope. The identification of genetic features specific to certain tumors may help establishing the correct diagnosis and, in some cases, may also indicate the potential use of targeted drugs in personalized medicine. The currently available techniques used for genetic testing are relatively costly and not available in several institutions. In this scenario, immunohistochemistry (IHC) may be one alternative method to detect genetic imbalances. Pan-Trk is an IHC marker that has been used to identify secretory carcinoma of the salivary glands (SC); NOR-1 is another IHC antibody previously found to be overexpressed in acinic cell carcinomas (ACC), which can resemble SC. Here, we analyzed both markers and established their baseline expression in a comprehensive group of SGC (n=119). Representative samples of paraffin-fixed tissue from each tumor were retrieved, organized in tissue microarrays (TMA) blocks, and stained with pan-Trk and NOR-1. We found that all SC cases were positive for pan-Trk; however, this marker was also positive in other SGC. NOR-1 staining was strong and diffuse in ACC cases; at the same time, other SGC showed weakly positivity for this marker. All SC cases were negative for NOR-1. Taken together, we conclude that NOR-1 is a specific and sensitive marker detecting ACC. On the other hand, the heterogeneous staining pattern for pan-Trk may limit its use in diagnosing SC. The use of both markers in combination may be an alternative approach for the distinction between SC and ACC.