The length of chemotherapy treatment is determined by a variety of factors. These include the type of cancer, the extent of cancer, the types of drugs that are given, as well as the expected toxicities of the drugs and the amount of time necessary to recover from these toxicities. Many chemotherapy treatment schedules (including the type and length of chemotherapy treatment) have been determined through clinical trials that compared them and determined which had the most benefit and was most well tolerated. In general, chemotherapy treatment is given in cycles. This allows the cancer cells to be attacked at their most vulnerable times, and allows the body's normal cells time to recover from the damage. There are really three issues regarding the cycle time, duration of the cycle, frequency of the cycle, and how many cycles.