Luminal ERα-expressing (ER+) human breast cancer cell lines, MCF-7, T47D, and ZR-75-1 (Figure 1A), each expressed TGFβ receptors II and I (TGFβRII and I, Figure 1A) at levels similar to those in bone-tropic MDA-MB-231 breast cancer cells (MDA-SA), an ER- cell line provided by Dr. Theresa Guise that forms TGFβ-dependent BMET in vivo [22,24,41]. Here, ESR1 is linked to breast cancer.