The involvement of CDC7 in DNA replication and DNA damage response was consonant with a potential dependency of SCLC on CDC7, as this cancer type is characterized by an exceptional highly proliferative index and universal inactivation of key tumor cell cycle checkpoint factors (i.e. TP53 and RB1) which might increase dependence on remaining intact regulators of cell cycle progression. This evidence concerns the gene RB1 and small cell lung carcinoma.