Several lines of evidence have demonstrated that in glioblastoma cell lines such as U-87 and U-251, downregulation of the expression levels of Cyclin B1 and cdc2 has been implicated in the G2/M arrest induced by various anticancer agents, including As2O3 (12, 14), active bufadienolide compounds such as hellebrigenin (19) and geldanamycin, an inhibitor of the chaperone activity of heat shock protein 90 (Hsp90) (49). The gene discussed is CCNB1; the disease is glioblastoma.