Clinical Application and Utility of Genomic Assays in Early-Stage Breast Cancer: Key Lessons Learned to Date

Early-stage hormone receptor–positive breast cancer is the most common subtype and stage presenting in countries with organized screening programs. Standard clinical and pathologic factors are routinely used to support prognosis and decisions about adjuvant therapies. Hormone receptor and HER2 status are essential for decision-making about the use of adjuvant hormonal and anti-HER2 therapies respectively. Genomic assays are now commercially available to aid in either further prognostication or in refining the potential benefit of adjuvant chemotherapy. The current genomic assays all generally quantify estrogen receptor and proliferation gene sets (among others) by rna expression, although the specific genes assayed are quite discordant. The present review focuses on the pivotal studies in which each assay attempted to demonstrate clinical utility, with an emphasis on prospective trial data for each assay, if available. Using genomic assays, health care providers will increasingly be able to individualize therapy or de-escalate therapy, optimizing clinic benefit while minimizing toxicities from systemic therapies.