Tumor necrosis factor-related weak inducer of apoptosis, TWEAK, is a TNF superfamily member that mediates signaling through its receptor fibroblast growth factor inducible-14, Fn14. In tumor cell lines, TWEAK induces proliferation, survival and NF-kappaB signaling and gene expression that promote tumor growth and suppress antitumor immune responses. Anti-TWEAK antibody, RG7212, inhibits tumor growth in vivo with decreases in pathway activation markers and modulation of tumor, blood and spleen immune cell composition. Candidate response prediction markers, including Fn14, have been identified in mouse models. Phase I pharmacodynamic data from patients are consistent with preclinical results. TWEAK:Fn14 signaling is upregulated in human cancer and pathway activation induces tumor proliferation and survival signaling. Blockade with anti-TWEAK mAb, RG7212, inhibits tumor growth in multiple models in mice. TWEAK induces changes that suppress anti-tumor immune responses and RG7212 blocks these effects resulting in changes in tumor immune cell composition and decreases in cytokines that promote immunosuppression. Antitumor efficacy in mice was observed in a range of Fn14 expressing models with pathway activation and expressing either wild-type or mutant p53, BRAF or KRAS suggesting both a patient selection strategy and potential broad clinical applicability. Preclinical mechanism of action hypotheses are supported by Phase I clinical data, with decreases in proliferation markers and increased tumor T cell infiltration.