With the chemotherapeutic agent cisplatin bound to DNA, damage to the molecule by electrons of low and high energies increases by factors varying from 1.3 to 4.4. The enhancement in bond dissociation is triggered by modifications of the interaction of low energy electrons with DNA. From our understanding of the latter, the present Letter attempts to explain the basic radiation-damage mechanism responsible for the efficiency of the concomitant chemoradiation treatment of cancer. Such a basic comprehension of the direct effects of radiation may have implications in the design of new chemotherapeutic and radiosensitizing drugs, as well as in the development of more efficient protocols in chemoradiation therapy. (C) 2009 Elsevier B. V. All rights reserved.