Polyploid giant cancer cells (PGCCs) have the properties of cancer stem cells, and cell-cycle-related proteins, including cyclin B1, CDC25B, and CDC25C play an important role in regulating the formation of PGCCs. This study shows that the phosphorylated proteins Chk2, and Aurora-A kinase regulate the expression and subcellular localization of cyclin B1, CDC25B, and CDC25C. The subcellular localization of these cell-cycle-related proteins is associated with pathologic grade and metastasis of tumors in cases of human breast cancer and ovarian cancer.