ESR1 and breast cancer: With more ER+ breast cancer patients utilizing the Oncotype DX assay, an overall decrease in the percentage of high-risk patients (from 9.6% in 2004 to 6.3% in 2015) and an increase in the percentage of low-risk patients (from 51% in 2004 to 61% in 2015) were observed (Fig. 2B).