Basics of Chemotherapy
Chemotherapy agents are medications that travel through the bloodstream and act against rapidly dividing cells. It is referred to as systemic treatment because it circulates through the bloodstream. Cancer cells grow and divide rapidly, but some normal cells also divide rapidly, and hence, may be temporarily affected by the chemotherapy drug. For example, when the agents circulate through the bloodstream they may affect normal blood cells, hair cells, and cells that line the mouth and intestinal tract. Side effects such as hair loss or nausea may occur for this reason.
Chemotherapy drugs are given in different schedules. Each time the drug or combination of drugs is given, it is called a cycle. Some may be given once every three weeks, while others are given once every two weeks or once a month. Some that are in pill form may be given daily with days off to provide a break. So, a twenty-one-day schedule means that you would get cycle number one on the first day and cycle number two on the twenty-first day and so on. Chemotherapy may cause a reduction in the white blood cells, perhaps hitting a low in two weeks; however, they may rebound back to normal by the third week, in time for the next treatment. Chemotherapy schedules are carefully designed to allow crucial normal cells enough time to recover, while repeating the treatment soon enough so that the cancer cells do not recover.
Some cancers are very sensitive to one chemotherapy drug, but not sensitive to others. Certain cancers may not be sensitive to a particular drug at a lower dose but may be sensitive to the same drug at higher doses. Sometimes cancers may start out being sensitive to a particular chemotherapy drug, but, after several treatments, the cancer cells develop resistance to that drug, thereby rendering it ineffective. If that is the case, the medical oncologist will alter your treatment and change to a different chemotherapy drug.