Insensitivity to standard clinical interventions, including chemotherapy, radiotherapy, and tyrosine kinase inhibitor (TKI) treatment, remains a substantial hindrance towards improving the prognosis of patients with non– small cell lung cancer (NSCLC). The molecular mechanism of therapeutic resistance remains poorly understood. The TNF-like weak inducer of apoptosis (TWEAK)–FGF-inducible 14 (TNFRSF12A/Fn14) signaling axis is known to promote cancer cell survival via NF-kB activation and the upregulation of prosurvival Bcl-2 family members. Here, a role was determined for TWEAK–Fn14 prosurvival signaling in NSCLC through the upregulation of myeloid cell leukemia sequence 1 (MCL1/Mcl-1). Mcl-1 expression significantly correlated with Fn14 expression, advanced NSCLC tumor stage, and poor patient prognosis in human primary NSCLC tumors. TWEAK stimulation of NSCLC cells inducedNF-kB–dependentMcl-1 protein expression and conferredMcl-1– dependent chemoand radioresistance. Depletion ofMcl-1 via siRNA or pharmacologic inhibition ofMcl-1, using EU-5148, sensitized TWEAK-treated NSCLC cells to cisplatinor radiation-mediated inhibition of cell survival. Moreover, EU-5148 inhibited cell survival across a panel of NSCLC cell lines. In contrast, inhibition of Bcl-2/BclxL function had minimal effect on suppressing TWEAK-induced cell survival. Collectively, these results position TWEAK–Fn14 signaling throughMcl-1 as a significant mechanism for NSCLC tumor cell survival and open new therapeutic avenues to abrogate the high mortality rate seen in NSCLC. Implications: The TWEAK–Fn14 signaling axis enhances lung cancer cell survival and therapeutic resistance through Mcl-1, positioning both TWEAK–Fn14 and Mcl-1 as therapeutic opportunities in lung cancer. Mol Cancer Res; 12(4); 550–9. 2014 AACR.