Shed HER2 surrogacy evaluation in primary breast cancer patients: a study assessing tumor tissue HER2 expression at both extracellular and intracellular levels

HER2 splice variants in breast cancer: investigating their impact on diagnosis and treatment outcomes

Overexpression of the HER2 receptor occurs in approximately 20% of breast cancer patients. HER2 positivity is associated with poor prognosis and aggressive tumour phenotypes, which led to rapid progress in HER2 targeted therapeutics and diagnostic testing. Whilst these advances have greatly increased patients' chances of survival, resistance to HER2 targeted therapies, be that intrinsic or acquired, remains a problem. Different forms of the HER2 protein exist within tumours in tandem and can display altered biological activities. Interest in HER2 variants in breast cancer increased when links between resistance to anti-HER2 therapies and a particular variant, Δ16-HER2, were identified. Moreover, the P100 variant potentially reduces the efficacy of the anti-HER2 therapy trastuzumab. Another variant, Herstatin, exhibits 'auto-inhibitory' behaviour. More recently, new HER2 variants have been identified and are currently being assessed for their pro- and anti-cancer properties. It is important when directing the care of patients to consider HER2 variants collectively. This review considers HER2 variants in the context of the tumour environment where multiple variants are co-expressed at altered ratios. This study also provides an up to date account of the landscape of HER2 variants and links this to patterns of resistance against HER2 therapies and treatment plans.

ELISA assay employing epitope-specific monoclonal antibodies to quantify circulating HER2 with potential application in monitoring cancer patients undergoing therapy with trastuzumab

Circulating HER2 extracellular domain (HER2 ECD) levels were proposed as a surrogate for HER2 tissue expression to monitor breast cancer patients for early relapse or responses to standard or HER2-targeted therapies, such as the monoclonal antibody (mAb) trastuzumab. Currently, available commercial ELISA assays for HER2 ECD rely on antibodies recognizing undisclosed or unknown epitopes. In this work, two ELISA assays employing MGR2 and MGR3 epitope-specific mAbs for HER2 ECD were developed and validated, showing good assay precision and linearity of the dose-response signal within the dynamic range of 0.19-12.50 ng mL^-1 and detection limits of 0.76 and 0.75 ng mL^-1 for the MGR2 and MGR3 assays, respectively. The developed assay showed a good agreement with two widely used commercial kits for HER2 ECD quantification in serum samples from breast cancer patients. A complete characterization of mAb-HER2 ECD interaction was performed by means of surface plasmon resonance using trastuzumab as control for both epitope mapping and kinetics analysis. The epitopes recognized by the two mAbs showed no overlap with trastuzumab, which was confirmed by trastuzumab interference analysis in serum samples. The method showed to be a practical approach to determine HER2 ECD with a high degree of sensitivity, reliability and recovery in samples containing mAbs-based therapies.