CAUSES OF CANCER

A. CARCINOGENS
One of the greatest risk factors for cancer is prolonged or repeated exposure to carcinogens—chemical, biological, or physical agents that cause the cellular damage that leads to cancer.

The details of how carcinogens cause cancer remain unclear.
One theory is that exposure to carcinogens, when combined with the effects of aging, causes an increase in chemicals in the body called free radicals.

An excessive number of free radicals causes damage by taking negatively charged particles called electrons from key cellular components of the body, such as DNA.
This may make genes more vulnerable to the mutating effects of carcinogens.

1. Tobacco smoke
2. Diet
3. Pathogens
4. Radiation
5. Environmental and Occupational chemicals

B. HEREDITARY FACTORS
Evidence suggests that heredity plays a role in developing cancer.
Some gene mutations associated with cancer are inherited.

For example, inheritance of the mutated tumor suppressor genes BRCA1 or BRCA2 greatly increases the risk of breast cancer in young women.
About 50 to 60 percent of women with inherited BRCA1 or BRCA2 mutations will develop breast cancer by the age of 70.

Inherited mutations in the genes MSH2, MLH1, PMS1, and PMS2, all of which repair DNA, are especially prevalent in a rare form of hereditary colon cancer.

Scientists suspect that many other hereditary factors contribute to cancer.
In addition to inherited mutations, other genetic variations, particularly those influencing how the body responds to carcinogens, may create a greater susceptibility to cancer.
The identities of the majority of these genetic variations are not yet known.

C. STEROID HORMONES
Medical research suggests that cancers of the reproductive organs may be affected by naturally occurring steroid hormones produced by the endocrine system.
These hormones stimulate reproductive organ cells to divide and grow.

In women, relatively high or long exposure to the female sex hormone estrogen seems to increase the risk of breast and uterine cancers.
Thus, early age at first menstruation, late age at menopause, having children after age 30, and never having children, all of which affect the duration of estrogen exposure in the body, increase the risk for these cancers.

Some evidence also suggests that estrogen replacement therapy (ERT), in which women take estrogen to offset the unpleasant effects of menopause, may also increase the risk of some cancers of the reproductive organs.
The risk appears to go down significantly, however, when estrogen and another female sex hormone, progesterone, are taken together.

At one time studies showed a link between birth control pills and cancer. However, these studies examined early forms of birth control pills, which contained high levels of estrogen.
Today’s birth control pills contain progesterone, as well as lower levels of estrogen, and carry very little risk of cancer.
Male sex hormones, particularly testosterone, also appear to play a role in cancers of the male reproductive organs, but this role is not yet well understood.

D. POPULATION DEMOGRHAPICS
Population studies show that a person’s age, race, and gender affect the probability that he or she will develop cancer.
Most cancers occur in adults middle-aged or older.
The risk of cancer increases as individuals age because genetic mutations accumulate slowly over many years, and the older a person is, the more likely that he or she will have accumulated the collection of mutations necessary to turn an otherwise healthy cell into a cancerous cell.

Women aged 20 to 29, for example, account for just 0.3 percent of all cases of breast cancer, but women over age 50 account for more than 75 percent of breast cancer cases.
Cancer of the prostate gland shows similar age discrimination.
According to the American Cancer Society (ACS) and the National Cancer Institute of Canada (NCIC), more than 75 percent of all prostate cancers are diagnosed in men who are over the age of 65.

Statistics show that men are more likely to develop cancer than women. In the United States, half of all men will develop cancer at some point in their lifetimes.
About one-third of all American women will develop cancer.
Cancer statistics for Canada are similar.
Stomach cancer is about twice as common in men than in women, as are certain types of kidney cancer.

However, the reasons for the discrepancy between the sexes are unknown.
Some cancers are more prevalent in particular races than others.
In the United States, for example, bladder cancer is twice as common in white people than it is in black people.
White women are slightly more likely to develop breast cancer than are black women, but black women are more likely to die of the disease.

Asian, Hispanic, and Native American women have the lowest breast cancer risk.
On the whole, African Americans, especially men, are more likely to develop cancer—and more likely to die from it—than members of any other group in the United States.
Reasons for the discrepancies between races are still not entirely clear, but many epidemiologists trace them to differences in diet and exercise, unequal access to medical care, and exposure to carcinogens.