PCNA and cancer: Therefore, a plethora of peptides mimicking the APIM or a sequence of caPCNA (“cancer-associated PCNA”) [28,37,38,39,40], targeting the PIP-box or caPCNA [41,42,43,44] were generated that selectively inhibit tumor cell growth, induce apoptosis, and enhance cytotoxicity of chemotherapy drugs on tumor cells.