Various reports have shown that DNA replication licensing factors, such as CDC6, CDT1 and MCMs, are overexpressed in different clinical tumor samples and tumor cell lines.12, 13, 14 Excess MCM proteins protect human cells from replication stress,9, 11 so tumor cells owning excess MCMs may act as a ‘shield' against chemical drugs which induce replication stress. Here, CDC6 is linked to neoplasm.