Although the precise causes of breast cancer are unclear, we know what the main risk factors are. Still, most women considered at high risk for breast cancer do not get it, while many who do have no known risk factors. Among the most significant factors are advancing age and a family history of breast cancer. Risk increases slightly for a woman who has had a benign breast lump and increases significantly for a woman who has previously had breast cancer or a history of endometrial, ovarian, or colon cancer.
A woman whose mother, sister, or daughter has had breast cancer is two to three times more likely to develop the disease, particularly if more than one first-degree relative has been affected. This is especially true if the cancer developed in the woman while she was premenopausal, or if the cancer developed in both breasts.
Researchers have now identified two genes responsible for some instances of familial breast cancer -- called BRCA1 and BRCA2. About one woman in 200 carries it. Having the gene predisposes a woman to breast cancer and -- while it does not ensure that she will get breast cancer -- her lifetime risk is 56%-85%. Because of this, risk prevention strategies and screening guidelines for those with the BRCA genes are more aggressive. There are other genes that have been identified as increasing the risk of breast cancer, including the PTEN gene, the ATM gene, and the CHEK2 gene. However, these genes carry a lower risk for breast cancer development than the BRCA genes.
Generally, women over 50 are more likely to get breast cancer than younger women, and African-American women are more likely than Caucasians to get breast cancer before menopause.
A link between breast cancer and hormones is gradually becoming clearer. Researchers think that the greater a woman's exposure to the hormone estrogen, the more susceptible she is to breast cancer. Estrogen tells cells to divide; the more the cells divide, the more likely they are to be abnormal in some way, possibly becoming cancerous.
A woman's exposure to estrogen and progesterone rises and falls during her lifetime, influenced by the age she starts and stops menstruating, the average length of her menstrual cycle, and her age at first childbirth. A woman's risk for breast cancer is increased if she starts menstruating before age 12, has her first child after 30, stops menstruating after 55, or has a menstrual cycle shorter or longer than the average 26-29 days. Current information about the effect of birth control pills and breast cancer risk is mixed. Some studies have found that the hormones in birth control pills probably do not increase breast cancer risk. However other studies suggest that the risk of breast cancer is increased in women who have taken birth control pills recently, regardless of how long she has taken them.
Some studies suggest that the use of hormone replacement therapy with estrogen and progesterone containing compounds increases the risk of developing breast cancers. The use of estrogens alone does not increase or decrease the risk unless they are used for prolonged periods of time and then the risk increases. The jury is still somewhat out on this matter though. Heavy doses of radiation therapy may also be a factor, but low-dose mammograms pose almost no risk.
The link between diet and breast cancer is debated. Obesity is a noteworthy risk factor, predominately in postmenopausal women, because obesity alters a woman's estrogen levels. Drinking alcohol regularly -- more than two drinks a day -- may also promote the disease. Many studies have shown that women whose diets are high in fat, either from red meat or high-fat dairy products, are more likely to get the disease. Researchers suspect that if a woman lowers her daily calories from fat -- to less than 20%-30% -- her diet may help protect her from developing breast cancer.
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