ESR1 and breast cancer: In line with these results, a study on TMAs of 601 breast cancer patients found a positive expression of RANK in 27% and of RANKL in 6% [30], and another large analysis of TMAs of 2299 breast cancer patients from four independent cohorts (of these 777 patients with ER-negative disease) showed even lower expression of RANK and RANKL in the tumor compartment [46].