Pan-TRK Immunohistochemistry Is Highly Correlated With NTRK3 Gene Rearrangements in Salivary Gland Tumors

Abstract

Aims: Secretory carcinoma (SC) is characterized by ETV6 rearrangements, most often ETV6-NTRK3 fusion. Given its histologic overlap with other salivary gland tumors (SGTs), SCs can be difficult to diagnose without genetic confirmation. A recently developed pan‐TRK (tropomyosin receptor kinase) antibody shows promise for identifying tumors with NTRK (neurotrophic tyrosine kinase receptor 3) fusions. The aim of this study was to evaluate the utility of pan‐TRK immunohistochemistry in distinguishing SCs from mimics and selecting patients eligible for TRK inhibitor clinical trials. We examined whole‐tissue sections from 111 SGTs with molecular characterization, including 26 SCs (23 with ETV6-NTRK3 fusion and 3 with ETV6-RET fusion detected by ligation-dependent reverse transcription-polymerase chain reaction, next-generation sequencing and 85 non-SC SGTs (no ETV6-NTRK3 fusion). Immunohistochemistry was performed with a pan‐TRK rabbit monoclonal antibody. When any pan‐TRK staining (nuclear or cytoplasmic with any staining intensity) was considered to indicate positivity, 22 of 23 SCs with ETV6-NTRK3 fusion (95.7%) and 33 of 85 non‐SC (38.8%) salivary neoplasms were positive, mainly basal cell adenoma, pleomorphic adenomas, adenoid cystic carcinomas, and epithelial-myoepithelial carcinomas. All SCs with ETV6-RET fusion were entirely negative. When only nuclear pan-TRK staining with any staining intensity was considered positive, 18 of 23 SCs with ETV6-NTRK3 fusion (78.3%) were positive, 11 among them with diffuse staining (>30% of cells). All non-SCs and SCs with ETV6-RET fusion were entirely negative. In comparison to molecular analysis (ligation-dependent reverse transcription-polymerase chain reaction, next-generation sequencing), nuclear pan-TRK IHC has a sensitivity of 78.3% and a specificity of 100% for diagnosing SCs with ETV6-NTRK3 fusion, 69% and 100% for SCs (all fusions). Pan-TRK is a reasonable screening test for diagnosing SCs among SGTs when taking only nuclear staining into account. Although pan-TRK expression is not entirely sensitive for SCs, nuclear staining is highly specific for SCs with ETV6-NTRK3 fusion. The lack of pan-TRK immunoreactivity in a subset of SCs is suggestive of atypical exons 4 to 14 or exons 5 to 14 ETV6-NTRK3 fusion or non-NTRK alternative fusion partners such as ETV6-RET. Pan-TRK staining can serve as a strong diagnostic marker to distinguish SC from it mimics and to select patients eligible for TRK inhibitor clinical trials.

Using pan-TRK and RET Immunohistochemistry for the Detection of Fusion Types of Salivary Gland Secretory Carcinoma

“…Nuclear staining is specific for SCs with ETV6-NTRK3 fusion, as cytoplasmic staining can also be present in tumors without NTRK3 fusions, such as basal cell adenoma, pleomorphic adenomas, adenoid cystic carcinomas, and epithelial-myoepithelial carcinomas. 13 Our study also demonstrated high sensitivity (96.3%) and specificity (100%) for pan-TRK IHC in the detection of ETV6-NTRK3 fusion-positive SCs. Compared with other NTRK fusion-positive tumors, nuclear staining is more important in SCs with ETV6-NTRK3 fusion.…”

“…Several studies have tested pan-TRK IHC using monoclonal antibodies (clone EPR17341) to identify NTRK rearrangement in different types of tumors. [9][10][11][12][13] Hechtman et al 9 reported that pan-TRK IHC sensitivity and specificity for NTRK fusions were 95.2% and 100%, respectively. All positive IHC cases had cytoplasmic staining, and half of the ETV6-NTRK3 fusions showed nuclear staining.…”

“…Bell et al12 found positive pan-TRK staining in 10 of 11 ETV6-NTRK3 fusion-positive SCs (sensitivity: 90.9%), and most had a nuclear staining pattern. Csanyi-Bastien et al13 tested pan-TRK staining in 111 salivary gland tumors including 26 SCs (23 with ETV6-NTRK3 fusion and 3 with ETV6-RET fusion), and found that nuclear pan-TRK IHC had a sensitivity of 78.3% and a specificity of 100% for diagnosing SCs with ETV6-NTRK3 fusion. Nuclear staining is specific for SCs with ETV6-NTRK3 fusion, as cytoplasmic staining can also be present in tumors without NTRK3 fusions, such as basal cell adenoma, pleomorphic adenomas, adenoid cystic carcinomas, and epithelial-myoepithelial carcinomas 13.…”

“…Bell et al12 reported that pan-TRK IHC had a sensitivity of 90.9% and specificity of 100% for SC with ETV6-NTRK3 fusion. Csanyi-Bastien et al13 demonstrated that pan-TRK IHC has a sensitivity of 78.3% and a specificity of 100% for diagnosing SCs with ETV6-NTRK3 fusion when nuclear staining was present. However, the application of RET IHC to identify RET fusion in lung and thyroid cancers showed disappointing results with high false-positive rates 17–23.…”

Recent Advances on Immunohistochemistry and Molecular Biology for the Diagnosis of Adnexal Sweat Gland Tumors

“…Immunohistochemistry: NTRK fusions can be detected by immunohistochemistry using a panTRK antibody (clone EPR 17341) with various performances and staining patterns, with a sensitivity up to 100% for secretory carcinoma [117][118][119]. When fusion involves ETV6, TRK immunohistochemistry is expected to stain the nucleus, while the cytoplasm and/or membrane are stained when alternative fusion partners are involved [120].…”