Reverse-phase protein microarray highlights HER2 signaling activation in immunohistochemistry/FISH/HER2-negative breast cancers.

EVALUATION OF: Wulfkuhle JD, Berg D, Wolff C et al. Molecular analysis of HER2 signaling in human breast cancer by functional protein pathway activation mapping. Clin. Cancer Res. 18(23), 6426-6435 (2012). Exhaustive characterization and mapping of pivotal molecules and downstream effectors deregulated in breast cancer is of fundamental clinical value to define the most effective therapy. Wulfkuhle et al. applied reverse-phase protein microarray, a highly sensitive immunoassay able to perform quantitative and multiplexed analysis of total and/or modified cellular proteins, to assess protein levels and activation/phosphorylation status of the HER family (EGFR, HER2, HER3) and downstream signaling molecules in HER2(+) and HER2(-) breast cancers. The research was performed using laser capture microdissected tumor epithelial cells from frozen samples and formalin-fixed paraffin embedded specimens, which were also analyzed by immunohistochemistry (IHC) and FISH. This study identified a subgroup of IHC/FISH/HER2(-) patients with HER2 activation/phosphorylation levels comparable with those obtained from IHC/FISH/HER2(+) tumors. HER2 signaling activation was independent from total HER2 expression and involved HER3 and EGFR activation. These findings indicate that molecular characterization by reverse-phase protein microarray of HER2 and its partners/effectors in the signaling cascade enables the identification of a subgroup of IHC/FISH/HER2(-) patients showing HER2 signaling activation. These patients, currently excluded from targeted therapy administration, could potentially benefit from this and it could improve prognosis and survival.