Surgery, radiation therapy, and chemotherapy have been applied to the curative therapy of 50% of cancer patients in the United States during the past 100 years. It is clear that the chemotherapeutic agents used to develop curative therapy for leukemias, lymphomas, gestational malignancy, and testicular cancer are not as active in the more numerous epithelial neoplasms, perhaps because of the complexity of genetic change in these latter neoplasms.