PCNA and neoplasm: The DNA repair pathway plays a role in tumor dissemination, and molecules such as poly (ADP-ribose) polymerase 1 (PARP1), NME/NM23 nucleoside diphosphate kinase 1 (NME1) and proliferating cell nuclear antigen (PCNA) are highly expressed in metastatic lesions (Fig. 2E, F).