ESR1 and breast cancer: Moreover, Ki-67 is one of the 21 prospectively selected genes of the Oncotype DXTM assay used to predict the risk of recurrence in a node-negative, tamoxifen-treated BC population enrolled in the National Surgical Adjuvant Breast and Bowel Project B-14 (NSABP B-14), as well to predict the magnitude of chemotherapy benefit in women with node-negative, estrogen receptor (ER)-positive BC enrolled in the NSABP B20 trial (Paik et al, 2004, 2006).