CANCER CAUSES AND PREVENTION

The vast majority of cancers are sporadic. There is no clear cause why one person gets cancer and another does not. Cancer develops over time when certain normal genes start mutating. Such cells multiply rapidly and become malignant. These gene mutations occur due to a complex mix of factors related to lifestyle, heredity and environment.

A risk factor is anything that increases a person`s chance of developing cancer. Different cancers have different risk factors. Use of tobacco, certain diets, alcohol, exposure to ultraviolet (UV) radiation, and to a lesser extent, exposure to cancer causing agents (carcinogens) in the environment and the workplace are some of the potential catalysts of cancer. It is important to remember, however, that these factors increase a person`s risk but do not always "cause" the disease.

Up to 85 per cent of cancers can be prevented by avoiding environmental risk factors like smoking, sun exposure, alcohol abuse and poor nutrition. Though age, race, gender and family history cannot be changed, knowing your personal cancer risk can help you devise a prevention strategy with regular screenings and healthy lifestyle choices. Having one or more risk factors for cancer doesn`t mean you will get cancer. In fact, many people considered high-risk never develop cancer while others with no known risk factors become ill.

Environmental Risk Factors

Radiation
High levels of radiation like those from radiation therapies and x-rays (repeated exposure) can damage normal cells and increase the risk of developing leukemia, as well as cancers of the breast, thyroid, lung, stomach and other organs.

Ultraviolet (UV) Radiation
UV radiation from the sun are directly linked to melanoma and other forms of skin cancer. These harmful rays of the sun cause premature aging and damage the skin. Artificial sources of UV radiation, such as sun lamps and tanning booths, also increase the risk of skin cancer. By wearing protective clothing and sunscreens and by avoiding prolonged exposure to the sun, one may reduce the risk of skin cancer. Many of the 1.3 million skin cancers diagnosed in the year 2000 could have been prevented by protection from the sun`s rays.

Viruses
Some viruses, including hepatitis B and C, human papillomaviruses(HPV), and the Epstein Barr virus, which causes infectious mononucleosis, have been associated with increased cancer risk. Immune system diseases, such as AIDS, can make one more susceptible to some cancers.

Chemicals
Long term exposure to chemicals such as pesticides, uranium, nickel, asbestos, radon and benzene can increase the risk of cancer. Such carcinogens may act alone or in combination with another carcinogen, such as cigarette smoke, to increase the risk of cancer and other lung diseases.

Tobacco
Cigarette smoking and regular exposure to tobacco smoke greatly increase lung cancer. Cigarette smokers are more likely to develop several other types of cancer like those of the mouth, larynx, esophagus, pancreas, bladder, kidney and cervix. Smoking may also increase the likelihood of developing cancers of the stomach, liver, prostate, colon and rectum. The use of other tobacco products, such as chewing tobacco, are linked to cancers of the mouth, tongue and throat. The risk of cancer decreases soon after a smoker quits, while precancerous conditions often diminish after a person stops using smokeless tobacco.

Alcohol
Heavy drinkers face an increased risk of cancers of the mouth, throat, esophagus, larynx and liver. Some studies suggest that even moderate drinking may slightly increase the risk of breast cancer. All cancers caused by cigarette smoking and heavy use of alcohol could be prevented completely. The American Cancer Society (ACS) estimated that in the year 2000 about 171,000 cancer deaths were expected to be caused by tobacco use, and about 19,000 cancer deaths were to be related to excessive alcohol use, frequently in combination with tobacco use.

Diet
High-fat, high cholesterol diets are proven risk factors for several types of cancer such as those of the colon, uterus and prostate. Obesity may be linked to breast cancer among older women as well as to cancers of the prostate, pancreas, uterus, colon and ovary. Many cancers that are related to dietary factors could be prevented. Healthy food choices and a well balanced diet including fiber, vitamins, minerals and low fat items may help to reduce cancer risk. Scientific evidence suggests that up to one-third of the 552,200 cancer deaths expected to occur in the US in the year 2000 were related to nutrition and other lifestyle factors. Certain cancers are related to viral infections-for example, hepatitis B virus (HBV), human papillomavirus (HPV), human immunodeficiency virus (HIV), human T-cell leukemia/lymphoma virus-I (HTLV-I), and others-that can be prevented through behavioral changes.

Others
Regular screening examinations by a health care professional can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, oral cavity, and skin at an earlier stage, when treatment is more likely to be successful. Self-examinations for cancers of the breast and skin may also result in detection of tumors at early stages. The screening-accessible cancers listed above account for about half of all new cancer cases.

The 5-year relative survival rate for these cancers is about 80%. If all Americans participated in regular cancer screenings, this rate could increase to 95%.

HereDitary Risk Factors
Twenty percent of cancers are hereditary. This means that the abnormal gene responsible for causing cancer is passed from parent to child, posing a greater risk for that type of cancer in all descendants of the family. However, just because someone has a cancer-causing gene doesn`t mean they will automatically get cancer. If hereditary cancer is suspected, family members should consider genetic counseling and testing to determine their risk. If diagnosed in the early stages, such cancers are most responsive to treatment.

Signs of hereditary cancer include:

Genetics
A theory exists with some scientific support, that certain smokers have a higher risk of smoking-induced lung cancer than others because of their genetic make-up.

Ethnic Groups
Some cancers are more common among certain ethnic groups.

Family History
Many cancers are associated with having a family history of that cancer. Breast, ovarian, prostate and colon are some of these cancers.

Several Relatives With Cancer
Cancer is such a common disease (with an estimated average of one case of cancer among every four people in the United States) that many families will have at least a few affected members. Approximately up to 15% of all cancers have a familial basis. That means that the cancer tends to occur among members of a family. Much of the time, different types of cancer occur apparently by chance, or in association with common family habits such as cigarette smoking. However, studies have suggested that certain cancers can occur to excess in some families. For example, a woman whose mother and/or sisters (first-degree relatives) had breast cancer, is 2-3 times more likely to develop breast cancer than a woman whose close female relatives have not had breast cancer.

Cancers That Are Common In Some Families A few types of childhood cancers are known to occur more often in some families. Researchers learned about how tumor suppressor genes work, through their study of retinoblastoma, a childhood cancer that originates in the eye. About 40% of children with retinoblastoma have inherited an abnormal Rb tumor suppressor gene from one parent. About 80% of children who inherit an abnormal Rb gene from a parent develop a retinoblastoma in one or both eyes.

Multiple Or Bilateral Cancers In Families In some families, cancers of one or more types develop in several family members significantly more often than the average cancer occurrence. Families with above average occurrence of breast cancer, for example, have been observed to have more cancers of the ovary, colon, or endometrium (body of the uterus) than expected.

Rare Or Unusual Types of Cancers Among Twins Leukemia rarely occurs in siblings. However, when an identical twin under 6 years of age has childhood leukemia, the probability that the other twin will develop the disease is about one in five, a magnitude of risk far exceeding the level in the general population.

Scientists are continuing to explore whether cancers in families develop only because of genes or also because of the environment that a family shares. Overall, genetically determined cancers tend to occur earlier in life than other cancers of the same type