Experimental evidence from our group (Buenrostro et al., <i>Bone</i> 113:77-88, 2018) suggests that tumor cells in the bone microenvironment early in disease rely more heavily on bone-derived growth factors, such as transforming growth factor-β (TGF-β), to sustain proliferation than tumor cells late in disease, which may grow independently of these factors. The gene discussed is TGFB1; the disease is neoplasm.