Cancer is a disease of the cells in the body. The body is made up from millions of tiny cells. Different parts of the body such as organs, bones, muscles, skin, and blood are made up from different specialized cells. All cells have a center called a nucleus which contains genes made from DNA. The genes control the functions of the cell.

Cancer is a complex group of diseases with many possible causes. Each cancer is thought to first start from one abnormal cell. What seems to happen is that certain vital genes which control how cells divide and multiply are damaged or altered. This makes the cell abnormal. If the abnormal cell survives it may multiply out of control into a cancerous (malignant) tumor.

Every individual have a risk of developing cancer. Many cancers seem to develop for no apparent reason. However, certain risk factors are known to increase the chance that one or more of your cells will become abnormal and lead to cancer. Risk factors include the following:




1. Chemical carcinogens

Several chemicals and environmental toxins are responsible for changes in normal cellular DNA. Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens. A carcinogen is something (chemical, radiation, etc.) which can damage a cell and make it more likely to turn into a cancerous cell.

  • Tobacco: If you smoke, you are more likely to develop cancer of the lung,mouth, throat, esophagus, bladder and  Smoking is thought to cause about 1 in 4 of all cancers. About 1 in 10 smokers die from lung cancer. Tobacco smoking is associated with many forms of cancer, and causes 90% of lung cancer. The heavier you smoke, the greater the risk. If you stop smoking, your risk goes down considerably.
  • Workplace chemicals: Such as asbestos, benzene, formaldehyde, etc. If you have worked with these without protection you have an increased risk of developing certain cancers. Prolonged exposure to asbestos fibers is associated with mesothelioma.

2. Lifestyle factors

Diet and other lifestyle factors can increase or decrease the risk of developing cancer. For example:

  • If you eat a lot of fruit and vegetables you have a reduced risk of developing certain cancers. The exact way in which they protect against cancer is not fully understood. These foods are rich in vitamins and minerals, and also contain chemicals called antioxidants. They may protect against damaging chemicals that get into the body.We should all eat at least five portions of fruit and vegetables per day.
  • Eating too much fatty food possibly increases the risk of developing certain cancers.
  • The risk of developing certain cancers is increased by obesity,lack of regular exercise, drinking too much alcohol and eating a lot of red meat.

3. Ionizing radiations

Radiation is a carcinogen. Radiations due to radon gas and prolonged exposure to ultraviolet radiation from the sun can lead to melanoma and other skin malignancies. The main concern is that radiation could increase the risk of cancers or harmful genetic effects. Radiation therapy given for one type of cancer may also cause another type of cancer. For example, those who receive chest radiation therapy for lymphomas may later develop breast cancer.

The probability of a radiation-caused cancer or genetic effect is related to the total amount of radiation accumulated by an individual. Any exposure to radiation can be harmful (or can increase the risk of cancer). But at very low exposures, the estimated increases in risk are very small. For this reason, cancer rates in populations receiving very low doses of radiation may not show increases over the rates for unexposed populations.




4. Infection

Some cancers can be caused by infections with pathogens. One research study estimated that about one in six cancers i.e. two million a year globally are caused by largely treatable or preventable infections. Notable among these include liver cancers due to Hepatitis B and C infections; cervical cancer due to infections with Human Papilloma virus (HPV); Epstein Barr virus causing Burkitt’s lymphoma and gastric or stomach cancer due to Helicobacter pylori infection. Four infections i.e. HPV, H. pylori, and hepatitis B and C viruses are accounted for 1.9 million cases of cervical, stomach and liver cancers in 2008. Immunization against HPV and hepatitis B are helping to combat these infections. But, most viruses and viral infections are not linked to cancer

5. Age

The older you become, the more likely that you will develop a cancer. This is probably due to an accumulation of damage to cells over time. Also, the body’s defenses and resistance against abnormal cells may become less good as you become older. For example, the ability to repair damaged cells, and the immune system which may destroy abnormal cells, may become less efficient with age. So, eventually one damaged cell may manage to survive and multiply out of control into a cancer. Most cancers develop in older people.

But the disease can occur at any age. For example, bone cancer is most frequently diagnosed among people under age 20, with more than one-fourth of cases occurring in this age group. And 10 percent of leukemia are diagnosed in children and adolescents under 20 years of age, whereas only 1 percent of cancer overall is diagnosed in that age group. Some types of cancer, such as neuroblastoma, are more common in children or adolescents than in adults.




6. Genetic or inherited cancers

Some cancers have a strong genetic link. For example, in certain childhood cancers the abnormal gene or genes which may trigger a cell to become abnormal and cancerous are inherited. Other types of cancer may have some genetic factor which is less clear-cut. It may be that in some people their genetic make-up means that they are less resistant to the effect of carcinogens or other factors such as diet. For examples: Inherited breast cancer and ovarian cancer genes including BRCA1 and 2. Li-Fraumeni syndrome includes defects in the p53 gene that leads to bone cancers, breast cancers, soft tissue sarcomas, brain cancers etc. Those with Down’s syndrome are known to develop malignancies such as leukemia and testicular cancer.

7. Hormonal changes

Notable among these are changes in the female hormone levels estrogen. Estrogens, a group of female sex hormones, are known human carcinogens. Although these hormones have essential physiological roles in both females and males, they have also been associated with an increased risk of certain cancers. For instance, taking combined menopausal hormone therapy (estrogen plus progestin, which is a synthetic version of the female hormone progesterone) can increase a woman’s risk of breast cancer. Menopausal hormone therapy with estrogen alone increases the risk of endometrial cancer and is used only in women who have had a hysterectomy.




8. Immune system dysfunction

Many people who receive organ transplants take medications to suppress the immune system so the body won’t reject the organ. These “immunosuppressive” drugs make the immune system less able to detect and destroy cancer cells or fight off infections that cause cancer. Infection with HIV also weakens the immune system and increases the risk of certain cancers.

Research has shown that transplant recipients are at increased risk of a large number of different cancers. Some of these cancers can be caused by infectious agents, whereas others are not. The four most common cancers among transplant recipients and that occur more commonly in these individuals than in the general population are non-Hodgkin lymphoma (NHL) and cancers of the lung, kidney, and liver. People with HIV/AIDS also have increased risks of cancers that are caused by infectious agents. HIV infection is also associated with increased risks of cancers that are not thought to be caused by infectious agents, such as lung cancer.

9. Sunlight

The sun, sunlamps, and tanning booths all give off ultraviolet (UV) radiation. Exposure to UV radiation causes early aging of the skin and skin damage that can lead to skin cancer. People of all ages should limit the amount of time they spend in the sun, especially between mid-morning and late afternoon, and avoid other sources of UV radiation, such as tanning beds. It is important to keep in mind that UV radiation is reflected by sand, water, snow, and ice and can go through windshields and windows.

The best way to lessen UV damage when spending time in the sun is to wear long sleeves, long pants, a hat with a wide brim, and sunglasses with lenses that absorb UV radiation. Sunscreen with a sun protection factor (SPF) of at least 15 may help prevent skin cancer but does not work as well as staying out of the sun and wearing protective clothing.




10. Environmental substances

Cancer is caused by changes to certain genes that alter the way our cells function. Some of these genetic changes occur naturally when DNA is replicated during the process of cell division. But others are the result of environmental exposures that damage DNA.

People can avoid some cancer-causing exposures, such as tobacco smoke and the sun’s rays. But others are harder to avoid, especially if they are in the air we breathe, the water we drink, the food we eat, or the materials we use to do our jobs. Scientists are studying which exposures may cause or contribute to the development of cancer. Understanding which exposures are harmful, and where they are found, may help people to avoid them.

Simply because a substance has been designated as a carcinogen, however, does not mean that the substance will necessarily cause cancer. Many factors influence whether a person exposed to a carcinogen will develop cancer, including the amount and duration of the exposure and the individual’s genetic background.




References:

www.cancer.gov

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