William D. DeWys, M.D.

In a previous editorial in this journal, Dr. Wittes discussed the initial phase of human studies of a new drug, studies which are aimed at establishing the optimal dose of the drug (Your Patient & Cancer, January 1982, page 24). The next step (Phase II) is aimed at testing the effectiveness of the new drug in a small series of patients. The effectiveness is most often evaluated by monitoring regression of measurable tumor using the criteria discussed by Dr. Carter in this issue (page 53). In general, if one studies 20 patients and observes at least one response, one can be reasonably certain that the actual response rate is probably greater than 15%. Thus one should study at least 20 patients to avoid falsely calling …