Although TOP2 poisons induce the degradation of both TOP2α and TOP2β, the rate and extent of degradation are much greater for TOP2β than for TOP2α (Fig. 2c and Fig. S1B)13, a finding that provides novel insight that may explain why the cytotoxic effects of most TOP2 poisons in tumor cells appear to be mainly TOP2α-dependent. This evidence concerns the gene TOP2B and neoplasm.