ESR1 and breast cancer: In order to test, if the previously identified EGFR/RANK-c interaction [10] and the reduced phosphorylation encountered in ER-negative, RANK-c positive breast cancer samples (Figure 1) has an impact in the response to EGFR-TKI treatment of ER-negative breast cancer cells, we employed MDA-MB-231 and SKBR3 cells stably expressing RANK-c.