2012). PCNA-I1, the most potent among the nine compounds, inhibits PCNA-dependent DNA synthesis in vitro (data not published) and DNA replication in tumor cells (Tan et al. 2012). The inhibitory effects of PCNA-Is on cell cycle distribution can be mimicked by knocking down PCNA expression (Tan et al. 2012). Moreover, PCNA-I1 selectively inhibits growth of tumor cells of various tissue origins (Tan et al. 2012). Here, PCNA is linked to neoplasm.