Our data, in line with other reports, show that inhibition of ATM by targeted drug application results in enhanced sensitivity to radiotherapy,23, 42, 43 recapitulating the radiosensitivity phenotypes of cells of patients with AT.4, 7, 30, 44 Moreover, in short-term in vitro assays, a therapeutic window for ATM inhibition appears to be present for ATM inhibition when the toxicity to non-cancer cells is taken into account. The gene discussed is ATM; the disease is ataxia telangiectasia.