The PALOMA-1/TRIO 18 study represents a global randomized phase II study that evaluated the combination in two cohorts of women with ER+/HER2− breast cancer: (1) selected for being ER+/HER2− (n = 66) and (2) selected for being ER+/HER2− as well as having the additional biomarkers of cyclin D1 amplification and/or loss of p16 (n = 99) [11]. This evidence concerns the gene ESR1 and breast cancer.