Bromodomain and extraterminal (BET) domain inhibitors (BETis) show efficacy on NUT midline carcinoma (NMC). However, not all NMC patients respond, and responders eventually develop resistance and relapse. Using CRISPR and ORF expression screens, we systematically examined the ability of cancer drivers to mediate resistance of NMC to BETis and uncovered six general classes/pathways mediating resistance. Among these, we showed that RRAS2 attenuated the effect of JQ1 in part by sustaining ERK pathway function during BRD4 inhibition. Furthermore, overexpression of Kruppel-like factor 4 (KLF4), mediated BETi resistance in NMC cells through restoration of the E2F and MYC gene expression program. Finally, we found that expression of cyclin D1 or an oncogenic cyclin D3 mutant or RB1 loss protected NMC cells from BETi-induced cell cycle arrest. Consistent with these findings, cyclin-dependent kinase 4/6 (CDK4/6) inhibitors showed synergistic effects with BETis on NMC in vitro as well as in vivo, thereby establishing a potential two-drug therapy for NMC.