Gene-Expression-Based Predictors for Breast Cancer.

An important and often complicated management decision in early stage hormone receptor (HR)-positive breast cancer relates to the use of adjuvant systemic chemotherapy. Although traditional clinicopathologic markers exist, tremendous progress has been achieved in the field of predictive biomarkers and genomics with both prognostic and predictive capabilities to identify patients who will potentially benefit from additional therapy. The use of these genomic tests in the neoadjuvant setting is also being studied and may lead to these tests providing clinical benefit even earlier in the disease course. Landmark articles published in the last few years have expanded our knowledge of breast cancer genomics to an unprecedented level, and mutational analysis via next-generation sequencing methods allows the identification of molecular targets for novel targeted therapeutic agents and clinical trials testing efficacy of targeted therapies, such as PI3K inhibitors, in addition to endocrine therapy for HR-positive breast cancer, are ongoing. We provide an in-depth review on the role of gene expression-based predictors in early stage breast cancer and an overview of future directions, including next-generation sequencing. Over the coming years, we anticipate a significant increase in utilization of genomic-based predictors for individualized selection and duration of endocrine therapy with and without genotype-driven targeted therapy, and a major decrease in the use of chemotherapy, possibly even leading to a chemotherapy-free road for early stage HR-positive breast cancer.