Population studies show that a personís 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 canceróand more likely to die from itóthan 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.