Cancer is the second most common cause of death in most of the countries (the first is heart disease), representing about one in five deaths. Cancer has become more common during the twentieth century, not because of population or radiation, but because cancer is more common in older people. As the number of older people in the population has increased , so has the frequency of cancer. The disease is very rare in people in their 20s, but the risk of developing cancer roughly doubles between ages 30 and 40 and doubles with each succeeding decade. This means that people in their 70s have twice the risk of cancer that people in their 60s have, and 16 times the risk of people in their 30s. However, great advances have been made in the diagnosis and treatment of cancer. 



Cancer is the unregulated growth and spread of cells. Cancer is not a single disease, it is a group of diseases in which a breakdown occurs in the normal processes that control th multiplication of cells. Almost all our cells need to be replaced regularly, some cells (such as those that line the intestine) divide every few hours and are shed after living for only a few days, other cells live for years. The processes of cell division and growth are controlled by genes that start and stop the growth process. Some of these growth controlling genes may undergo changes (mutation) that cause them to malfunction. 
Cell growth is then uncontrolled, the cell divides, forming more cells with the same mutated genes. Simple overgrowth of cells may lead to a relatively harmless, benign (not likely to spread0 tumor such as a wart or polyp, but two or three (or more) genes within a single cell may undergo changes that cause a growth that becomes malignant, (likely to spread) and invades and damages blood vessels, nerves, and other body tissues. Invasion of healthy tissues by the growth of malignant tumor cells is called metastasis. it usually take 10 years or more for a malignant symptoms. Malignant tumor cells may be carried by the bloodstream or spread through the lymphatic system to all parts of the body, where they form other tumors. Once a cancer has metastasized (spread) it is usually incurable. However, treatment can prolong and improve the quality of life. 


The three major causes of changes in growth controlling cells include viruses, chemical, and radiation. Several human viruses have been shown to cause cancer. For example, the hepatitis B virus causes a type of liver cancer, some papilloma viruses are closely linked with cancer of the cervix, and another virus is responsible for a rare type of leukemia. The most significant chemical cause of cancer is tobacco, smoking is the cause of most lung cancers and is an (continued on coming pages). 
Important factor in canners of the tongue, larynx, esophagus, cervix, and bladder. Chewing tobacco can cause mouth and tongue cancer. Workers who are exposed to chemicals such as benzene, coal tar, rubber, and some plastic can develop cancers of the blood cells, kidneys, bladder and liver. Radiation from radioactive isotopes X rays, and nuclear waste can cause cancer, especially some types of leukemia. The main radiation hazard is sunlight, which causes most skin cancers. People with fair skin that is repeatedly exposed to excessive amounts of direct sunlight have an increased risk of developing skin cancer. 
These factors do not, however, always cause cancer in everyone who is exposed to the risk, for example, only a minority of people who have ever smoked cigarettes get lung cancer (although many others die prematurely of chronic illnesses such as heart diseases and emphysema). In part, this is because some people are genetically more or less susceptible development of cancer include the amount of alcohol that you drink and the ability of your body's immune system to detect and destroy cancer cells at an early stage. 



The key to curing some types of cancer is early diagnosis and treatment. Successful treatment is far less likely once malignant cells have spread from the original tumor to form cancers in other parts of the body. 
Tests currently used to detect cancer are designed to achieve early diagnosis. Mammography, for example, detects possible breast tumors in women when such tumors are still too small to be found by physical examination of the breasts tumor is under half an inch in diameter at diagnosis. 
Regular Pap smears in women detect precancerous changes in the cervix at an early stage when treatment is simple and effective. The death rate from cancer of the cervix has fallen dramatically in recent years in communities where most women have regular Pap smears. 
There is evidence that regular examination of the intestine (colon) in people over age 50 improves survival from cancers of the rectum and colon. 
When cancer is suspected, imaging techniques reveal accurate details of tumors, increasing the chances of successful treatment; these chances of successful treatment; these techniques include CT scans, MRI scans, and radio nuclide scans including PET scan. Also, many internal organs can now be examined directly by endoscopy (examination with a viewing tube). 
Advances have been made in treatment as well as in diagnosis of cancer. Drugs may be injected directly into the arteries that supply blood to a tumor, thereby allowing a more targeted destruction of the tumor. In addition, reconstructive plastic surgery offers the possibility of restoring a person's appearance after major sugary on the breast, head or neck. Some forms of chemotherapy and treatment with hormones are more effective and less difficult for the patient than treatments used in the past. For example, tamoxifen, the drug used most commonly to treat breast cancer, has few major side effects in most women. Radiation therapy, too has become more precise and therefore is more effective and causes fewer side effects. 


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