Novel markers to detect HER2 amplification in Breast cancer

Overexpression of HER2 in breast cancer is an important prognostic and predictive biomarker, assessed using immunohistochemistry (IHC) and in situ hybridization (ISH). More than 20% of tumours are graded equivocal on IHC and is send for reflex testing via ISH. In situ hybridization (ISH) is an expensive assay and is not available widely in resource limiting areas. Therefore, we propose that genes found significantly co-expressed with HER2 in breast cancer can be used as surrogate markers for HER2 in breast cancer which can detect HER2 positivity on IHC itself. This hypothesis is based on analysis of publicly available datasets from the Gene Expression Omnibus (GEO) database. The genes found most significantly correlated with HER2 expression were PGAP3 (r = 0.85), GRB7 (r = 0.82), STARD3 (r = 0.78), CDK12 (r= 0.68), PSMD3 (r= 0.67) and GSDMB (r = 0.63). We hypothesize that these identified surrogate markers for HER2 amplification which can be detected on IHC can detect HER2 amplification status in HER2 equivocal tumors based on IHC staining alone and will reduce the number of HER2 2+ (equivocal) category tumours.