G.MATHE Institut de Cancerologie et d'Immunogenetique (INSERM et Association Claude-Bernad), H6pital Paul-Brousse and Institute Gustave-Roussy, Villejuif 20 years ago, the main, if not only object of the cancer therapist was to effect complete surgical exeresis or radiotherapeutic destruction of a local tumor, or to obtain, by means of chemotherapy, an "apparently complete regression" of a local or disseminated neoplasia. Today it is realized that (a) at the time of the operation or radiotherapy, two patients in every three carrying an apparently localized tumor have a few cancer cells...