Cessation of treatment in advanced cancer. A major responsibility for all physicians, but particularly for oncologists, is to recognize the time when active antitumor treatment ceases to have a rational basis. The decision to treat or not to treat at any stage of disease requires an analysis of "the legitimate aims of therapy." We have acquired the ability to cure or prolong survival in an increasing proportion of patients with several types of cancer. For patients who fail to achieve those results and for those with tumors that are rarely amenable to specific therapy, the choice of less surely effective therapy is an option; the patient must participate in the decision, armed with as much information and insight as possible, for conventional and experimental treatment. A distinction must be made between specific antitumor therapy and palliative measures for which cessation is never an option. Happily, cessation of treatment must also be considered when therapy has been so successful that the patient has achieved complete remission. At what point may treatment be discontinued without the danger of relapse? These issues are rarely crisply defined, but primary concern for the patient and careful analysis of the available data can lead to appropriate value judgements. 