At present, we are investigating whether SENP1 and/or SENP2 are indeed TopoIIα deSUMOylating enzymes; whether a molecular link between geminin-induced TopoIIα phosphorylation, SUMOylation and deSUMOylation exists; and whether using inhibitors of deSUMOylating enzymes in combination with TopoIIα-directed drugs could be used to treat breast cancers with high geminin levels. This evidence concerns the gene GMNN and breast cancer.