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Cancer chemotherapy remains an intriguing area of pharmacology. On the one hand, use of anticancer drugs produces high rates of cure of diseases, which, without chemotherapy, result in extremely high mortality rates (eg, acute lymphocytic leukemia in children, testicular cancer, and Hodgkin's lymphoma). On the other hand, some types of cancer are barely affected by currently available drugs. Furthermore, as a group, the anticancer drugs are more toxic than any other pharmaceutic agents, and thus their benefit must be carefully weighed against their risks. Many of the available drugs are cytotoxic agents that act on all dividing cells, cancerous or normal. The ultimate goal in cancer chemotherapy is to use advances in cell biology to develop drugs that selectively target specific cancer cells. A few such agents are in clinical use, and many more are in development.
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Cancer cell population kinetics and the cancer cell cycle are important determinants of the actions and clinical uses of anticancer drugs. Some anticancer drugs exert their actions on cells undergoing cycling (cell cycle-specific [CCS] drugs), and others (cell cycle-nonspecific [CCNS] drugs) kill tumor cells in both cycling and resting phases of the cell cycle (although cycling cell are more sensitive). CCS drugs are usually most effective when cells are in a specific phase of the cell cycle (Figure 54–1). Both types of drugs are particularly effective when a large proportion of the tumor cells are proliferating (ie, when the growth fraction is high).
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