Comprehensive analysis of HER2 status through genomic, transcription, and translation among 5,305 patients with diverse malignancies.

Abstract

3632 Background: HER2 alterations is a predictive biomarker for anti-HER2 regimen. Success in breast and gastric cancers with anti-HER2 therapies translated to explore their efficacy in other tumors. Currently, measurement of HER2 can be done by assessing the expression of protein [e.g. immunohistochemistry (IHC)] or gene amplification of copy number variation (CNV) [e.g. fluorescence in situ hybridization or next-generation sequencing (NGS)]. But little is known about the transcription level (mRNA) of HER2. Herein, we investigated HER2 mRNA expression and its association with gene and protein expressions among diverse cancer types. Methods: Between 2015-2019, HER2 status was evaluated using IHC, qRT-PCR and NGS by Paradigm Diagnostics (CLIA-certified laboratory). All tumors in the database were included for analysis. Correlations between all 3 tests were done. An illustrative patient who was treated with anti-HER2 therapy base on the mRNA testing is presented. Results: HER2 testing was performed on 5305 patients (pts) with diverse cancers including NSCLC (n=1175), breast (n=1040) and colon (n=566); 4.1% (161/3926) had amplification through NGS, 33.3% (615/1848) had mRNA overexpression and 9.3% (236/2533) had overexpression by IHC. Of 723 pts who had all three tests performed, we found 7.5% (54/723) of pts with all three HER2 markers being positive (CNV [+]/mRNA [+]/ IHC [+]). Meanwhile, variety of amplification/ expression patterns were seen (see Table). CNV positivity translated to protein expression in 95% of cases. While only 4% of pts were IHC positive when CNV and mRNA were negative. 20% (144/723) of pts had mRNA overexpression alone among diverse cancer types. Representative case of 70yo female with metastatic cholangiocarcinoma harboring mRNA overexpression (but negative for CNV, IHC unclear due to sample insufficiency) who had near complete response to anti-HER2 therapy with progression-free survival of 24+ months is presented. Conclusions: HER2 status can be discordant with different assays but NGS positivity has excellent correlation with mRNA and protein expression. Of importance, HER2 mRNA can be overexpressed in 20% of pts even when gene amplification and protein expression are negative. Further studies are warranted to determine the clinical utility of mRNA as a biomarker for HER2 and potential use for anti-HER2 targeted therapies. [Table: see text]