TNF and osteosarcoma: Although we did not formally test the requirement for TNFα in order for Smac mimetics to exert anti-osteosarcoma effects in our model, this conclusion is consistent with our data showing that (a) Smac mimetic sensitivity of osteosarcoma cells in vitro depended on exogenous TNFα, (b) Smac mimetics retarded growth of tumors derived from these cells in vivo, and (c) implanted osteosarcomas contained TNFα that was produced by intratumoral immune cells.