How Can Chemotherapy Treat Cancer

Because chemotherapy is a systemic treatment (affecting the en¬tire body), it can be used to treat either a localized tumor or the entire body, if the tumor has been metastasized. A single drug is used in some instances, but most chemotherapy regimens include a combination of three or four drugs that kill cancer cells in different ways. These drug combinations are administered according to a clearly specified schedule, or protocol. Because many different treatments are available, your doctor will discuss with you the regimen that is appropriate for your cancer. You won’t necessarily need detailed knowledge about the drugs used in chemotherapy to make an appropriate treatment decision.

During your treatment, your oncologist will monitor your progress using the same methods that were used during the diagnostic and staging studies.

Drug Classifications
How different anticancer drugs kill cancer cells or prevent them from dividing depends on their classification. Drugs in the same class kill the cancer cells by the same mechanism of action: that is, they all attack the same target within the cell. Most drug regimens are composed of drugs from different classes; the different drugs work in different phases of cell division or on different targets. For example, some drugs are incorporated into DNA and prevent cell division, others will cross-link the strands of DNA making it impossible for the cell to duplicate the DNA, others will inhibit key enzymes involved in the cell cycle or DNA synthesis, and still others may prevent the cell from undergoing mitosis by inhibiting the mitotic spindle needed to separate the chromosomes. Newer drugs work by inhibiting cell signaling pathways or by blocking the action of growth factors. There are other drugs that are designed to enhance the efficacy of the more standard chemotherapy agents (modifiers or sensitizers) and still others that can reduce the toxicity of treatment (protectors). Combination chemotherapy regimens are designed so that drugs will work in concert so that it is difficult for the cancer cell to become resistant to therapy.

Some of the common chemotherapy regimens used to treat different types of cancer. Regimens are sometimes given acronyms using the first letter of the chemical or trade name of each drug. For example, note that two of the four regimens available for Hodgkin's disease are MOPP and ABVD. Doctors use these abbreviations to communicate more easily. Because the names of some different drugs begin with the same first letter, the abbreviations don t always indicate which drugs are in a particular regimen.

Risk of Late Complications Relative Risk

In any group of people, there is a risk that some of them will develop cancer during their lifetime. This risk is called the expected number of cancers. When the number of cured cancer patients who develop secondary cancers later in life is calculated, the result is the observed number of cancers.

To calculate the relative risk, the number of observed cases is divided by the number of expected cases:

Observed cases Relative risk =- Observed cases / Expected cases

Statistical methods are then applied to see whether more former patients than expected developed secondary cancers some years after their first cancer was cured. For example, let's say a group of 1,000 adults were cured of Hodgkin's disease when they were young adults. Fifteen years later, we find that 36 of these former patients have developed leukemia, but we expected only 4 people in 1,000 who have never had Hodgkin's disease to develop this leukemia. Therefore, to determine the relative risk that former Hodgkin's patients will develop leukemia later in life, we would divide 36 by 4, which is 9. In other words, there are 9 times more cases of leukemia than we would have expected.

Although the relative risk of 9 seems high, only 36 (about 3.5%) of the 1,000 patients developed this complication, whereas 964 did not, and 4 of the 1,000 patients would have developed leukemia whether they had had Hodgkin's disease or not. There¬fore, only 32 (about 3%) of 1,000 patients developed leukemia because of their earlier Hodgkin's disease or its treatment.