While the cause of breast cancer is not clear, some major risk factors are known to exist. Most women at high risk for breast cancer do not develop breast cancer, while many women with no known risk factors for breast cancer do eventually develop breast cancer. Among the most notable factors are increasing age and family history. Some women with benign breast lumps also have an increased risk of developing cancer, and women with prior breast or ovarian cancer have a significantly increased risk of developing cancer.
A woman’s risk of breast cancer is 2 to 3 times higher if her mother, sister, or daughter has had breast cancer, especially if there is more than 1 first-degree relative with breast cancer. Researchers have identified two familial breast cancer susceptibility genes – BRCA1 and BRCA2 – and about 1 in 200 women carry one of these genes. Having the BRCA1 or BRCA2 gene makes a woman more susceptible to breast cancer, but not necessarily to breast cancer.
Usually, women over 50 are more likely to get breast cancer than younger women.
The relationship between breast cancer and hormones is very clear. Researchers believe that the more estrogen a woman has in her body, the more likely she is to develop breast cancer. Estrogen promotes cell division, and the more cells that divide, the more likely they are to have some degree of abnormality and therefore may become cancerous.
Estrogen and progesterone levels rise and fall throughout a woman’s life, influenced by the age at which she starts and stops menstruating, the average length of her menstrual cycle, and her age at first birth. The risk of breast cancer increases if a woman starts menstruating before age 12, has her first child after age 30, stops menstruating after age 55, or has a shorter or longer than average menstrual cycle of 26 to 29 days. Breast cancer risk may be slightly higher in women who have recently taken birth control pills. This risk disappears if the pill has not been taken for at least 10 years. Some studies have suggested that treating menopause with a combination of estrogen and progestin hormone replacement therapy may increase the risk, especially if it has been more than 5 years. However, this determination is somewhat outdated. High-dose radiation therapy may also be a risk factor, but low-dose mammograms pose little risk.
There has been a lot of discussion about the relationship between diet and breast cancer. Obesity is a risk factor that requires special attention, and regular alcohol consumption, especially more than 1 drink per day, also increases the risk of breast cancer. Many studies have shown that a high-fat diet increases the risk of breast cancer. Researchers speculate that if women reduce their fat intake to less than 20% to 30% of their daily calorie source on a regular basis, they will reduce their breast cancer risk.