Chemotherapy consists of drugs used to treat cancer. There are more than hundred drugs used today, according the American Cancer Society. (Reference 1) Doctors decide what will be in chemotherapy based on the kind and the stage of cancer the patient has, the patient's overall health and the latest research. (References 1 and 2) Still, it is impossible to predict the outcome of therapy for any individual.
Chemotherapy Drugs
Chemotherapy drugs can be used to cure a specific cancer, control tumor growth when cure is not possible, shrink tumors, destroy cancer cells that are left after surgery or to relieve symptoms such as pain. (Reference 2) Doctors often use combination chemotherapy---combine different drugs for more effective treatment, keeping in mind the actions and side effects of each drug. (Reference 3)
How Chemotherapy Works
Cancer cells originate from our healthy cells, which gained the ability to multiply and lost the ability to die. (Reference 1) Chemo drugs can kill those cancer cells, because they aim at destroying fast-dividing cells. They affect important parts of cells, such as DNA. (References 2 and 3) There are several groups of chemo drugs according to how they kill the cancer cells. (Reference 2)
Alkylating Antineoplastic Agents And Nitrosureas
Alkylating agents are able to damage DNA. Cancer cells are more sensitive to DNA damage due to their fast multiplication, lack of time to correct the damage and lack of damage-repair machinery. Some of the alkylating agents are cyclophosphamide, hexamethylmelamine, busulfan, procarbazine and oxaliplatin. (References 2 and 3)
Nitrosureas act similarly to alkylating agents, interfering with enzymes that help repair DNA. (Reference 3) Their advantage is that they can travel into the brain, unlike many other chemotherapy drugs, what makes them useful for treating brain tumors. (Reference 2) They include carmustine and lomustine. (References 2 and 3)
Antimetabolites
Antimetabolites are drugs very similar to normal substances within the cell. Since cells mistakenly incorporate such substances into their metabolism, they stop dividing. Methotrexate interferes with folic acid---essential vitamin important for synthesis and repair of DNA. Pyrimidine analogues---5-fluorouracil and foxuridine---interfere with pyrimidines, one of the building blocks of DNA. 6-Mercaptopurine and 6-Thioguanine interfere with purines, also building blocks of DNA. (Reference 2)
Topoisomerase Inhibitors
Toposiomerase inhibitors interfere with the action of specific enzymes---topoisomerases---necessary for DNA replication, which cells need to multiply. There are two topoisomerases, and topoisomerase I inhibitors include ironotecan, topotecan and topoisomerase II inhibitors include amsacrine and etoposide. (Reference 2)
Naturally Derived Chemo Medications
Plant alkaloids are made from certain types of plants. Vincristine, vinblastine, paclitaxel and docetaxel block cell division by preventing function of microtubules---cell parts vital for cell division. Etoposide, irinotecan and topotecan act as topoisomerase inhibitors. (Reference 2) Antitumor antibiotics are antibiotics derived from the soil fungus Streptomyces. They either break up the DNA strands or inhibit DNA synthesis that cells need to grow. Some of the antitumor antibiotics are actinomycin, plicamycin and mitomycin. (References 2 and 3)
Side Effects
Since chemo drugs aim at destroying fast-multiplying cells, they cannot distinguish between cancer and healthy cells that multiply rapidly. (Reference 2) The cells most commonly affected by chemotherapy are blood cells, cells in the mouth, stomach and bowel cells and hair follicles. That leads to low blood counts, mouth sores, nausea, diarrhea and hair loss. Different drugs may affect different parts of the body.
