[Radio-chemotherapy combinations: from biology to clinics]

Combination of radiotherapy and chemotherapy (CRC) is actually one important way of research in oncology. Theoretical advantages are: 1) Spatial cooperation; 2) Additivity, which is only obtained if the toxicity of each modality are different; 3) Supra-additivity, which needs a rigorous in vitro definition; the only way to prove it is to make an isobologram analysis. This model has however, some limitations: qualitative variable could not be used, results could be different, depending on the cell line and isoeffect chosen... In fact, a supra-additivity was only demonstrated for cisplatinum and etoposide. Interactions mechanisms were: 1) at the molecular level, creation of new lesions or inhibition of radiation lesions repair; 2) At the cellular level, either cytokinetic cooperation with S-phase dependent drugs, or synchronisation for the drugs which blocked the cells in M-phase; 3) At the tissular level, reoxygenation, cycle redistribution... In clinical practice, three mains schedules have been described: sequential, alternating and concomitant. Only the latter try to use the supra-additivity phenomena. Aims of CRC could be: improvement or in survival or in local control, preservation of an functional organ... Depending on the tumor site and aim of the CRC, some schedules had to be preferred. For head and neck cancers, alternating or concomitant schedules offer a better local control. In bronchial carcinomas, sequential administration of the two modalities reduce the metastatic rate, but not the local control. Concomitant schedule improve the local control rate only. In some conservative protocol of bladder cancers, sequential and concomitant administration were used. In conclusion, CRC begins to be the usual clinical practice. The present schedules could be improved with the help of laboratory findings, which are now more and more precise.