Molecular imaging of HER2-positive breast cancer: a step toward an individualized 'image and treat' strategy.

Abstract

HER2 overexpression is correlated with aggressive tumor behavior and poor clinical outcome. Therefore, HER2 has become an important prognostic and predictive factor, as well as a target for molecular therapies. The article reviews recent advances in molecular imaging of HER2 that could facilitate individual approaches to targeted therapy of HER2-positive breast cancers. Because of the heterogeneity of breast cancer and possible discordance in HER2 status between primary tumors and distant metastases, assessment of HER2 expression by noninvasive imaging may become an important complement to immunohistochemistry or fluorescence in-situ hybridization analyses of biopsied tissue. Monoclonal antibodies such as trastuzumab and pertuzumab, or small scaffold proteins such as affibody molecules are used as HER2-targeting agents. For imaging purposes, these agents are labeled with positron or gamma-emitting radionuclides, optical dyes, or paramagnetic contrast molecules for positron emission tomography single photon emission tomography optical, and magnetic resonance imaging, respectively. HER2-specific molecular probes, combined with modern imaging techniques to provide information on HER2 expression not only in primary tumors but also in distant metastases not amenable to biopsy, may reduce problems with false negative results and, thereby, influence patient management by selecting patients that would benefit from HER2-targeted therapies. The new 'image and treat' strategy, involving assessment of target presence and distribution in an individual patient followed by optimized, target-specific drug delivery, may potentially improve efficacy of cancer treatment while reducing side effects.