A theory of the action of cancer chemotherapeutic drugs.

This paper presents an analysis of the results of cancer therapy, based on the histories of treated and untreated cancers taking into account the biology of immunity and drug action. Cancer chemotherapeutic drugs in addition to a direct action on the malignant cells, act on the host's immune system. The importance of tumour–host interactions in determining the overall progress of the tumour is emphasized. It is postulated that in the early stages of therapy, remission occurs because the drug is given at a time when the host has either some degree of immunity against the tumour, or has a reversible immune tolerance with respect to the tumour antigen. In contrast, in the later stages of treatment, immunity against the tumour is depressed and this is a major cause of therapeutic failure.