Breast cancer occurs when normal cells within breast tissue undergo genetic and cellular changes that cause them grow uncontrollably and form tumors. One in eight women will develop breast cancer in their lifetime, according to the American Cancer Society. While the exact causes of breast cancer are not known, a number of genetic and lifestyle factors are known to contribute to breast cancer.
Female Hormone Levels
According to the American Cancer Society, women are 100 more times likely to develop breast cancer than men. This is in large part due to the female sex hormones progesterone and estrogen, which can help to signal for the growth of breast tumors. Accordingly, a women's overall lifetime exposure to estrogen and progesterone will influence risk for breast cancer. Women who experience early puberty or late menopause will have higher lifetime estrogen exposure and are more at risk for developing breast cancer. Likewise, women who have multiple pregnancies will have fewer menstrual cycles over their lifetime, less estrogen exposure and lower risks for breast cancer. Progesterone replacement therapies for women who have had hysterectomies or experienced menopause can also increase breast cancer risk.
Breast Cancer Genes
A number of specific genetic changes are associated with breast cancer. The American Cancer Society explains that the BRCA1 and BRCA2 genes are often mutated in women with breast cancer. In fact, women who inherit mutated BRCA genes have up to an 80 percent risk of developing breast cancer. The gene HER2 also has an important role in many breast cancers. The HER2 gene is often multiplied through gene duplication in breast tumors. This increases growth signals to breast tumor cells. Once a woman is diagnosed with breast cancer, the HER2 status of the tumor will be determined and designated as "HER2-positive" or "HER2-negative." This will help to determine how to best treat the tumor.
Recent Use of Birth Control
The Mayo Clinic and the American Cancer Society explain that use of birth control pills can increase breast cancer risk. This risk decreases when use of birth control stops.
Obesity
The National Cancer Institute explains that body fat levels can increase estrogen levels and breast cancer risk. Menopausal women who are obese are especially at risk for developing breast tumors.
Alcohol
The American Cancer Society explains that women who drink more than two alcoholic drinks per day have a greater chance of developing breast cancer compared to women who drink one drink per day or less. The Mayo Clinic and the American Cancer Society recommend that women limit alcohol intake to one drink per day or less.
