Notably, several other components of the DDR pathway were increased in SCLC, including the checkpoint kinases CHK1 and CHK2, the ataxia telangiectasia related protein ATR, and the DNA-dependent protein kinase catalytic subunit DNA PKcs, which may be important to maintain cell viability in light of high replication stress (Figure 1). This evidence concerns the gene CHEK1 and small cell lung carcinoma.