ARTICLE ABSTRACTGlobal miRNA functional screens can offer a strategy to identify synthetic lethal interactions in cancer cells that might be exploited therapeutically. In this study, we applied this strategy to identify novel gene interactions in KRAS-mutant cancer cells. In this manner, we discovered miR-1298, a novel miRNA that inhibited the growth of KRAS-driven cells both in vitro and in vivo. Using miR-TRAP affinity purification technology, we identified the tyrosine kinase FAK and the laminin subunit LAMB3 as functional targets of miR-1298. Silencing of FAK or LAMB3 recapitulated the synthetic lethal effects of miR-1298 expression in KRAS-driven cancer cells, whereas coexpression of both proteins was critical to rescue miR-1298–induced cell death. Expression of LAMB3 but not FAK was upregulated by mutant KRAS. In clinical specimens, elevated LAMB3 expression correlated with poorer survival in lung cancer patients with an oncogenic KRAS gene signature, suggesting a novel candidate biomarker in this disease setting. Our results define a novel regulatory pathway in KRAS-driven cancers, which offers a potential therapeutic target for their eradication. Cancer Res; 76(19); 5777–87. ©2016 AACR.