TGFB1 and breast cancer: To examine the effects of TGF-β on our tumor-bone invasion model, we implanted the mouse mammary tumor cell line CL66M2 into two different sites in female mice, under the dorsal skin flap over the calvaria and into a subQ lesion, and then injected the mice six times with TGF-β receptor 1 kinase inhibitor (R1-Ki) over the course of the experimental period (Figure 1A).