CDKN2A and neoplasm: However, the two tumors expressing high p16ink4a and normal CDK4 levels, (S23 and S27), showed some initial response to the CDK4 inhibitor, but after ending the treatment, tumor growth recovered to an even faster rate than that of the untreated tumors, and the survival of the treated mice was very similar to that of the untreated controls (Figure 6).