Chemotherapy, frequently abbreviated as "chemo," is a type of cancer treatment that employs one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) in a standard regimen. Chemotherapy may be administered with the intention of achieving a cure, which almost always involves the use of combinations of drugs, or it may be employed with the aim of prolonging life or reducing symptoms, a process known as palliative chemotherapy. Chemotherapy is one of the principal areas of medical practice devoted to the pharmacological treatment of cancer, which is referred to as medical oncology. The term chemotherapy now encompasses the nonspecific use of intracellular poisons to inhibit mitosis (cell division) or to induce DNA damage (thereby enabling DNA repair to augment chemotherapy). This definition excludes the more selective agents that block extracellular signals (signal transduction). Therapies that target specific molecular or genetic pathways, inhibiting growth-promoting signals from classic endocrine hormones (primarily estrogens for breast cancer and androgens for prostate cancer), are now referred to as hormonal therapies. Other inhibitions of growth signals, such as those associated with receptor tyrosine kinases, are classified as targeted therapy.
Drugs (like chemo, hormone therapy, or targeted therapy) are used to treat cancer in a way that affects the whole body. They enter the bloodstream and can target cancer cells anywhere in the body. This type of therapy is often used with other local treatments, such as radiation, surgery, and hyperthermia.
The way traditional chemotherapeutic agents work is by interfering with cell division (mitosis), but cancer cells vary a lot in how susceptible they are to these agents. In essence, chemotherapy is a way of damaging or stressing cells, which may then lead to cell death if apoptosis is initiated. A lot of the side effects of chemotherapy can be traced back to damage to normal cells that divide quickly and are therefore sensitive to anti-mitotic drugs. These include cells in the bone marrow, digestive tract and hair follicles. This is why you often see side effects like myelosuppression (which means there are fewer blood cells, so the immune system is also affected), mucositis (inflammation of the digestive tract lining) and alopecia (hair loss). Because they affect immune cells (especially lymphocytes), chemotherapy drugs are often used to treat diseases that result from the immune system attacking the body's own tissues (autoimmunity). These include rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, vasculitis and many others.
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