In vitro functional analysis of HER2 variants in lung cancers to evaluate their oncogenic activity and predict clinical response to HER2 targeted therapies.

Abstract

e23150 Background: HER2 variants are implicated as oncogenic drivers in a variety of cancers. However, not all HER2 variants found on next-generation sequencing (NGS) have been studied, raising the question if these variants of unknown significance (VUS) are oncogenic. This study explores the use of an in-vitro functional assay on HER2 and other variants found on NGS in patients (pts) with lung cancer, and its predictive value for response to HER2 targeted therapy. Methods: Pts with lung cancer at Memorial Sloan Kettering identified to have a HER2 variant by NGS on MSK IMPACT are eligible. NGS data on HER2 variants and co-mutations were analyzed. Functional status was determined by the NovellusDx FACT platform. Mutations were synthesized and transfected into HeLa cells with a fluorescently tagged signaling pathway reporter (MAPK, NFKB, JAK-STAT). Fluorescent microscopy quantified the translocation of reporters to the nucleus, inferring gain of function. Afatinib was added and its effect on pathway activation analyzed. Functional information was correlated with clinical outcomes. Results: As of 2/1/17, 13 pts were included, 9 unique HER2 variants analyzed. Known activating HER2 mutations analyzed (exon 20 insertions (A775_G776insYVMA, G778_P780insGSP, G776delinsVC), point mutations (V659E, L755P, S301F)) showed in vitro gain of function. HER2 VUS analyzed included D277Y showed no gain of function; exon 16 splice variant c.1889 showed gain of function. Afatinib was added to 4 cell lines with gain of function variants (G778_P780insGSP, V659E, L755P, exon 16 splice variant c.1889) all had inhibited pathway activation suggesting in vitro sensitivity to afatinib. Clinically, no response was seen in 2 pts treated with afatinib but more pts are planned to be treated. Objective responses to ado-trastuzumab emtansine (NCT02675829) were seen in 5 pts, all of which had HER2 variants with gain of function. Conclusions: In vitro functional analysis of HER2 variants based on NGS reports is feasible, and has the potential to identify novel actionable oncogenic drivers from VUS. Its predictive value for clinical response to targeted therapy requires further study.