Using a bioluminescent model where the expression of luciferase is under the control of the TGF-β signaling pathway, Korpal et al. [269] found that TGF-β signaling is activated in breast cancer cells in murine bone metastases, and that inhibition of bone resorption with a bisphosphonate decreased the corresponding luciferase signal, confirming that TGF-β released from the bone during osteoclastic resorption is the main source of TGF-β for cancer cells in bone. Here, TGFB1 is linked to breast cancer.