Abstract
The purpose of this essay is to focus on some of the difficulties in starting and completing well designed therapeutic experiments in the field of cancer. Failure to appreciate the nature and complexity of therapeutic trials in human beings, I believe, has hindered progress in treatment research and can continue to serve as a roadblock to exploiting current opportunities at a critical time in the history of the effort to control cancer.The backbone of therapeutic experiments is knowledge of the natural history of disease. The effect of the experiment on the natural history of disease is the result observed. . . .