Most commonly, chemotherapy acts by killing cells that divide rapidly, one of the main properties of cancer cells. This means that it also harms cells that divide rapidly under normal circumstances: cells in the bone marrow, digestive tract and hair follicles; this results in the most common side-effects of chemotherapy–myelosuppression (decreased production of blood cells), mucositis (inflammation of the lining of the digestive tract) and alopecia (hair loss).
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Most commonly, chemotherapy acts by killing cells that divide rapidly, one of the main properties of cancer cells. This means that it also harms cells that divide rapidly under normal circumstances: cells in the bone marrow, digestive tract and hair follicles; this results in the most common side-effects of chemotherapy–myelosuppression (decreased production of blood cells), mucositis (inflammation of the lining of the digestive tract) and alopecia (hair loss).
Other uses of cytostatic chemotherapy agents (including the ones mentioned below) are the treatment of autoimmune diseases such as multiple sclerosis and rheumatoid arthritis and the suppression of transplant rejections (see immunosuppression and DMARDs). Newer anticancer drugs act directly against abnormal proteins in cancer cells; this is termed targeted therapy.
History
see: History of cancer chemotherapy
The usage of chemical substances and drugs as medication can be traced back to the ancient Indian system of medicine called Ayurveda, which uses many metals besides herbs for treatment of a large number of ailments. More recently, Persian physician, Muhammad ibn Zakarīya Rāzi (Rhazes), in the 10th century, introduced the use of chemicals such as vitriol, copper, mercuric and arsenic salts, sal ammoniac, gold scoria, chalk, clay, coral, pearl, tar, bitumen and alcohol for medical purposes.
The first drug used for cancer chemotherapy, however, dates back to the early 20th century, though it was not originally intended for that purpose. Mustard gas was used as a chemical warfare agent during World War I and was studied further during World War II. During a military operation in World War II, a group of people were accidentally exposed to mustard gas and were later found to have very low white blood cell counts. It was reasoned that an agent that damaged the rapidly-growing white blood cells might have a similar effect on cancer. Therefore, in the 1940s, several patients with advanced lymphomas (cancers of certain white blood cells) were given the drug by vein, rather than by breathing the irritating gas. Their improvement, although temporary, was remarkable. That experience led researchers to look for other substances that might have similar effects against cancer. As a result, many other drugs have been developed to treat cancer, and drug development since then has exploded into a multibillion-dollar industry. The targeted-therapy revolution has arrived, but the principles and limitations of chemotherapy discovered by the early researchers still apply.
Principles
Cancer is the uncontrolled growth of cells coupled with malignant behavior: invasion and metastasis. Cancer is thought to be caused by the interaction between genetic susceptibility and environmental toxins.
In the broad sense, most chemotherapeutic drugs work by impairing mitosis (cell division), effectively targeting fast-dividing cells. As these drugs cause damage to cells they are termed cytotoxic. Some drugs cause cells to undergo apoptosis (so-called "programmed cell death").
