PCNA and cancer: Currently, the development of targeted cancer therapies are actively investigated against KIAA0101/p15PAF by agents with inhibitory functions similar to KIAA0101 tv2 [28], against p53 by anti-mutant p53 agents or MDM2/4 antagonists [49, 50], against Ki-67 by exploitation of MKI67 promoter to drive the expression of siRNAs or therapeutic genes [51], and against PCNA by inhibitors targeting to the modified PCNA involved in DNA repair [52].