GMNN and breast cancer: These data show that endogenous geminin overexpression in breast cancer cell lines such as MDAMB231 prevents the persistence of TopoIIα on chromosomes in a CKIε-dependent (positively) and Cdc7-dependent (negatively) manner, thus reducing the ability of the TopoIIα poison (for example, etoposide) to covalently bind TopoIIα to DNA.