Whereas the CDK4/6 inhibitor PD0332991 proved less effective to chemosensitize SCLC cells to CPT analogs, the CDK inhibitors CDK4I, roscovitine and olomoucine gave comparable chemosensitization effects in combination with 9AC, SN38, rubitecan and to a lesser extent with TPT and CPT109, not directly related with topoisomerase mRNA expression. Here, CDK4 is linked to small cell lung carcinoma.