Breast cancer is the second most common cancer of women in the United States, after skin cancer. According to the American Cancer Society, about one in eight women will develop breast cancer, and about one in 35 will die from this disease. The exact causes of breast cancer are not fully understood, however, a number of factors are known to contribute to breast cancer risk.
Female Hormones
Simply being a woman is one of the biggest factors contributing to breast cancer. While it is possible for men to get breast cancer, women are 100 times more likely to develop breast cancer than men. The American Cancer Society explains that this is because female hormones estrogen and progesterone play an important role in the growth of breast tumors.
Age
According to the Mayo Clinic, age is also a factor involved in the onset of breast cancer. Women over the age of 60 have a higher risk of developing this cancer compared to younger women. This increased risk is in part due to changes in hormone levels that occur after menopause. The likelihood of developing mutations in breast cancer genes also increases with age.
Family History
Many of the factors that contribute to breast cancer are of a genetic origin. According to the American Cancer Society, about 10 percent of breast cancers are the result of inherited genes that help to promote breast cancer onset. It is common for women with breast cancer to have inherited a mutated copy of the BRCA1 or BRCA2 gene from their parents. Mutations in this gene put women at a high risk for breast cancer.
Hormonal Factors
A number of factors that affect estrogen or progesterone levels can influence breast cancer risk. According to the National Cancer Institute, lifetime exposure to estrogen can increase a woman's risk for breast cancer. This is thought to explain why women with multiple pregnancies are at a lower risk for breast cancer as they have fewer menstrual cycles and less lifetime estrogen exposure. Late menopause can also increase lifetime exposure to estrogen and increase breast cancer risk.
Recent Use of Birth Control
The American Cancer Society explains that recent use of birth control pills can increase risk for breast cancer. This risk decreases after use of birth control has stopped.
Lack of Exercise
Women who exercise for more than 30 minutes at least four times a week are at reduced risk for breast cancer. The National Cancer Institute explains that this may be due to decreased estrogen levels in response to exercise.
Obesity
Being overweight can increase a woman's risk for breast cancer. The American Cancer Society explains that this risk is especially pertinent to women who have undergone menopause. Fat can provide a source of estrogen, and after menopause fat provides the sole source of estrogen for women. Having more fat increases estrogen levels and can increase risk for breast cancer.
Alcohol
The American Cancer Society and the Mayo Clinic explain that alcohol use can be a contributing factor to breast cancer. It is recommended that women at risk for breast cancer limit alcohol use to one drink per day.
