Characterization of tumor mutational burden in LKB1 mutant lung tumors

Inactivating mutations in LKB1/STK11 are present in ~20% of non-small cell lung cancers (NSCLC) and portend poor response to anti-PD-1 immunotherapy in patients and genetically engineered mouse model (GEMMs). Here, we sought to uncover the basis for immunotherapy resistance of these tumors and to define strategies that overcome this barrier. Whereas high tumor mutational burden (TMB) often correlates with response to anti-PD1 treatment, we found that LKB1-deficient NSCLCs from non-smokers and GEMMs exhibited striking elevations in nonsynonymous mutations compared to LKB1 wildtype tumors. Correspondingly, LKB1 mutant NSCLC cell lines showed defects in both replication dependent and independent double-strand DNA break (DSB) repair, which were reversed upon LKB1 re-expression.