Questions are posed regarding the marked differences in clinical response of different types of cancer to chemotherapeutic agents in the light of the quite similar sensitivity of many different types of cancer cells to such agents when they are exposed in logphase cultures in vitro (the cell-culture paradox). Thymidine index data, cell-culture response data, data on the relative sensitivity of "resting" vs. log phase leukemia cells and in vivo tumor responses are presented. Consideration of these diverse results suggest that biochemical differences exploited by some chemotherapeutic agents often may be largely quantitative-associated with the ratio of proliferating to nonproliferating cells in a normal or neoplastic tissue-thus the ratio of cells carrying out vulnerable biochemical reactions to cells not carrying out vulnerable biochemical reactions when both are exposed to drug in vivo.
- Why do different types of human cancer respond so differently to different classes of drugs in vivo and why do different types of animal cancer respond so differently to different classes of drugs in vivo and why do specific types of animal cancer sometime behave much more like specific types of human cancer than do other types of human cancer? T o put it From the Kettering-Meyer L~boratory (Affiliated with Sloan-