ESR1 and breast cancer: Furthermore, we found that the TNBC cell lines (MDA-MB-231 and Hs578T) which endogenously express KISS1R also robustly express AXL (Fig. 6B), but the ERα-positive breast cancer cells (T47D and MCF7), that barely express KISS1R, do not express AXL (Supplementary Fig. 5).