Abstract P1-07-03: Quantification of HER2 expression at the single cell level and HER2 intratumoral heterogeneity of breast cancer tissue samples using automated image analysis

HER2 is an important biomarker for breast and gastric cancer prognosis and patient treatment decisions. HER2 positivity, as defined by IHC or FISH testing, remains an imprecise predictor of patient response to HER2-targeted therapies. Challenges to accurate HER2 assessment and patient stratification may include intratumoral heterogeneity, lack of assays that are quantitative and/or objective, and differences between measuring HER2 at the protein vs. DNA level. We have developed a novel immunofluorescence method for absolute quantitation of HER2 protein expression at the single cell level on formalin-fixed, paraffin-embedded (FFPE) patient samples. Our assay utilizes automated image analysis software to identify cells, classify them as tumor or non-tumor cells, and quantitate the level of HER2 staining for each tumor cell. The HER2 staining level is then converted to absolute HER2 receptor numbers per cell using an array composed of cell lines that span a range of HER2 levels. This cell pellet array standard is stained in parallel with each tissue sample. With this approach we quantitate HER2 expression at the single cell level and describe the heterogeneity of HER2 expression within breast cancer tissue samples. Our assay provides additional insight into the absolute level of HER2 expression and heterogeneity of HER2 expression within tumors, and allows for direct comparison with the currently existing HER2 assessments by standard IHC and/or FISH. This new assay could be used to increase understanding of the relationship between HER2 expression and patient response to HER2-targeted therapies. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-07-03.