[en] The paradox in the title is described on recent findings concerning the effects of anti-angiogenetic drugs on possible radiation resistance and sensitivity of tumor tissue. Suppression of angiogenesis leads to inhibition of tumor growth, based on which anti-tumor drugs like anti- vascular endotherial growth factor (VEGF) antibody bevacizumab to suppress the genesis have been developed and clinically used, but they conceivably increase the population of hypoxic tumor cells. Those drugs are essentially used in combination with other chemotherapeutic agents and/or radiation. Hypoxic tumor cells present in the tissue are generally radioresistant. There are reported findings, however, that the drugs sometimes elevate the efficacy of radiotherapy, which hypothesizes that the drugs induces a proangiogenetic state, where increased level of growth factors in the tissue is reduced to normalize the vasculature and thereby reoxygenation occurs, the oxygen effect. Because copper is a cofactor of growth factors like VEGF and basic fibroblast growth factor (bFGF) and essential for angiogenesis, authors have studied the effect of a Cu-chelator, trientine, on transplanted mouse tumors which has been shown to induce apoptosis of the target cells. Combination of the chelator with X-ray irradiation is found effective in tumor growth inhibition and in survival increase. For more effective combination therapy, the interaction occurring in combinations of regimen should be elucidated. (R.T.)