Cancer is a disease in which body cells grow uncontrollably because their normal regulatory mechanisms have been damaged. Of the many types of cancer, the majority form solid tumours in a specific part of the body, commonly the skin, breast, lung, bowel, or prostate gland. The disease may then spread through the blood and lymphatic systems. As our understanding of cancer has advanced during the past 25 years, changes in lifestyle, efficient screening programmes, and new types of therapy have improved prevention and treatment of the disease.
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The term “cancer” comes from the Greek word for crab. The ancient Greek physician Hippocrates likened a spreading cancerous tumour to the shape of a crab’s claw. Although our understanding of the disease has advanced dramatically since then, the description is still apt. An important feature of a cancerous tumour is its ability to spread within the body.
Genetic basis of cancer
The discovery in the late 1970s that damage to genetic material underlies cancer was one of the most important breakthroughs in cancer research. Every cell contains genetic information in the form of about 20,000–25,000 genes that control the activities of cells. A cell may become cancerous when certain genes that control vital processes such as cell division become damaged. These faulty genes may be inherited or caused by carcinogens (cancer-causing agents), such as sunlight and tobacco smoke. Cells are continually exposed to carcinogens, but they rarely become cancerous for several reasons: cells can usually repair their damaged genes; more than one gene must be damaged before cancer develops; and the body’s immune system often destroys any abnormal cells before they are able to multiply enough to form a cancerous tumour.
Aging and cancer
Cancer is most common among older people, largely because their cells have had more time to accumulate genetic damage, but also because the body’s defences against cancer, particularly the cells and proteins of the immune system, gradually become less efficient with age. In addition, a cancer that began earlier in life may not be diagnosed until old age because it often takes many years for some types of tumour to grow large enough to produce noticeable symptoms. Since life expectancy increased significantly in developed countries during the second half of the 20th century, cancer has now become one of the most common causes of death in the UK, second only to cardiovascular disease.
For 2,000 years, doctors have attempted to cure cancer by surgically removing visible tumours. For some localized cancers, radiotherapy can be effective; this treatment is often combined with surgery with the aim of achieving a cure. Treatment with anticancer drugs, known as chemotherapy, may be used instead of or in combination with surgery to destroy cancers that have spread around the body.
New therapies for the treatment of cancer that are currently being assessed include inactivating damaged genes and boosting the immune system’s ability to destroy cancerous cells. However, as with many other diseases, the most effective ways to lower the number of deaths are currently prevention through a healthy lifestyle and screening to detect cancer early.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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