A group of drugs used to destroy or slow the growth of cancerous cells
Cancers are a broad group of diseases in which abnormal body cells form and multiply, interfering with the function of surrounding tissues. Cancerous cells may affect vital organs and can spread to other parts of the body through the bloodstream. Anticancer drugs either destroy the cancer cells or prevent them from spreading. Treatment with these drugs, which is known as chemotherapy, is normally managed by an oncologist, a doctor who is a specialist in the medical treatment of cancer.
Anticancer drugs may be given with the aim of curing the cancer, prolonging life, or relieving symptoms. In some cases, chemotherapy is used in combination with surgery and/or radiotherapy. Anticancer drugs may be used to shrink the tumour before the other treatments, or they may be used after surgery or radiotherapy to prevent the growth of cancer cells that may have spread around the body.
The group of drugs most commonly used to treat cancer are cytotoxic drugs, which damage or destroy both cancerous and healthy body cells. Some hormonal drugs, such as the synthetic female sex hormones medroxyprogesterone and megestrol, are also used to treat certain forms of cancer, as are hormone antagonist drugs, which work by blocking the effects of hormones that stimulate cancer growth. Other anticancer drugs include drugs that stimulate the immune system and drugs that disrupt specific biological processes of cancer cells.
There are several types of cytotoxic drug, which kill cells or prevent cancer cells from increasing in number. The drugs either act directly on the cells’ genetic material, DNA, or prevent the cells from using the nutrients they need to divide normally. The effect of the drugs is concentrated on areas of tissue where cells are rapidly dividing, and they are therefore effective in treating rapidly growing cancers, such as those of the lymphatic system (see Lymphoma), various forms of leukaemia, many childhood cancers, and some types of cancer of the testis. Some cytotoxic anticancer drugs, such as methotrexate, are also used to treat noncancerous conditions such as severe psoriasis and rheumatoid arthritis. Cytotoxic drugs are usually administered in hospital. Several short courses of the drugs are given over a number of weeks, with drug-free periods in between to allow time for the normal body cells to recover.
Cytotoxic drugs can cause severe side effects because they affect any area of the body where there is rapid cell division, including the bone marrow, the hair follicles, and the lining of the mouth and the intestines. Damage to the bone marrow may reduce the numbers of red and white blood cells and platelets in the blood. Some anticancer drugs may also cause folic acid deficiency. These problems can lead to anaemia, an increased susceptibility to infection, and reduced ability of the blood to clot. Nausea and vomiting are particularly common side effects of cytotoxic drugs and may be severe. Certain drugs may cause mouth ulcers and hair loss.
The severity of many side effects can be reduced by additional treatment with other drugs. For example, antiemetic drugs are commonly given and are usually effective in preventing vomiting. Most side effects are temporary and do not result in long-term damage. However, some types of cytotoxic drug can cause irreversible damage to the ovaries, which leads to premature menopause, or to the testes, resulting in abnormal or reduced sperm production. Men who wish to have children in the future can arrange to have their sperm frozen and stored before treatment. For women, the harvesting of ovarian tissue or eggs for future use is a possibility.
If you are taking cytotoxic drugs, you will have regular blood tests, including a blood count, before each course of treatment to measure the levels of different types of blood cell. See your doctor at once if you develop new symptoms, such as a sore throat, because they may indicate a low number of white blood cells.
Treatment with hormones may be suitable for certain types of cancer whose growth is influenced by hormones. This type of treatment may be used following surgery or radiotherapy to prevent any remaining cancer cells from growing and spreading. The treatment may involve the use a hormone that halts the progression of the cancer. For example, megestrol is used to slow the progression of cancer of the uterus.
Alternatively, a hormone antagonist drug may be used. Drugs of this type oppose the effects of the hormone that stimulates the growth of the cancer. For example, hormone antagonists such as tamoxifen are often effective in halting the progression of certain types of breast cancer that are stimulated by the female sex hormone oestrogen. The drug blocks the action of oestrogen on breast cells. The growth of cancerous cells that have spread from a cancer in the prostate gland may be slowed by using the drug goserelin, which blocks the secretion of the male sex hormone testosterone.
Hormonal drugs are usually taken orally or injected, and sometimes treatment is continued for several years. Most of these hormonal drugs have milder side effects than cytotoxic drugs. However, treatment with tamoxifen slightly increases the risk of developing cancer of the uterus; you should report abnormal vaginal bleeding to your doctor immediately.
These drugs include biological agents (sometimes called simply “biologicals”), which are being used increasingly in the treatment of cancer. Some biologicals work by stimulating the immune system against cancer, whereas other work by disrupting specific biological processes of cancer cells, thereby inhibiting their growth or destroying them.
Biologicals that are thought to work primarily by stimulating the immune system include aldesleukin, used to treat some advanced kidney cancers; and interferon alfa (see Interferon drugs), which may be used to treat several types of cancer, including certain lymphomas, leukaemias, malignant melanomas, kidney tumours, and AIDS-related Kaposi’s sarcoma. Biologicals that work primarily by disrupting cancer cells’ biological processes include bevacizumab, used to treat some breast cancers; cetuximab (some bowel cancers); erlotinib (some lung cancers); lapatinib (some breast cancers); sorafenib (some kidney and liver cancers); and sunitinib (some kidney cancers). Rituximab is a monoclonal antibody that may be used to treat some lymphomas and leukaemias. It is not known exactly how it works.
Side effects vary according to the specific drug. Generally, however, common side effects include fever, muscle aches, vomiting, fatigue, rash, and diarrhoea. More serious side effects, such as heart, liver, or blood disorders, may also occur and therefore these drugs are given under specialist supervision.
Many anticancer drugs are potentially harmful to a developing fetus. You should consult your doctor about your contraception needs before starting treatment.
Anticancer drugs (chemo-therapy) may be given in a series of treatments. The drugs kill cancer cells, but they also destroy some normal cells. For this reason, there are recovery periods between treatments during which the number of normal cells is allowed to rise again. Treatment is stopped when no cancer cells are detectable.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.