Breast cancer is a common form of cancer among women in the United States, Canada and Europe. However, in Africa and Asia, the prevalence is much lower, indicating the possibility of environmental triggers as well as a genetic predisposition.
While the number one risk factor is simply being female, other risk factors include:
- Age. Breast cancer occurs more often in women over 50 and is less common in premenopausal women. Nearly 80 percent of all newly diagnosed invasive breast cancer cases occur in women aged 50 and older, according to the American Cancer Society (ACS).
- Family history. Women with family history of breast cancer have a greater risk of developing the disease. The risk is highest when the breast cancer occurs in a first-degree relative (mother, sister or daughter) and when the cancer occurs before age 50. A family history of ovarian cancer also increases the risk of breast cancer in women.
- Genetic factors. Inheriting mutations or alterations of certain genes called BRCA1 and BRCA2 increases the risk of developing breast cancer. The ACS estimates that 5 to 10 percent of breast cancer cases result from inherited mutations of these genes. A woman with these genes has an 80 percent chance of developing breast cancer in her lifetime, according to the ACS. Women with a family history of breast cancer may be tested for the mutated gene. However, interpretation of the test results and decisions about treatment are complicated. Recent studies have identified other genes and gene mutations that may be associated with breast cancer. Several studies have shown nearly 200 gene mutations that are associated with some breast tumors.
- Ashkenazi Jewish heritage. This segment of the population has a higher incidence of the BRCA 1 and 2 genes and a higher prevalence of breast cancer.
- Previous history of breast cancer or of benign breast tumors. This includes being diagnosed with breast cancer as well as noncancerous tumors. Research has demonstrated the risk of developing breast cancer varies with the actual type of benign breast disease found in a woman.
- Race. Breast cancer is more common in white women than in those of other races, including Hispanic, Asian or black American. Race also affects the survival rate of breast cancer patients. White women with breast cancer have a 90 percent chance of surviving five years. African American women, however, have a 76 percent chance of surviving five years. The difference in survival may be attributed to later stage diagnosis and poorer treatment options. In addition, recent studies have indicated that African American women may be more likely to get a form of breast cancer that is less responsive to treatment.
- Hormone factors. Hormones may increase the risk of breast cancer. Hormonal influences that are believed to raise the risk include:
- Early menarche. Women who started their period before 12 years of age.
- Late menopause. Women who go through menopause after age 55.
- Hormone drugs. The use of oral contraceptives has been linked to a slight increase in breast cancer risk. However, women who have stopped using oral contraceptives for 10 years or more share the same risk as those women who never used them. Hormone replacement therapy (HRT) that uses a combination of estrogen and progestin may increase a woman's risk. The risk increases with the length of use. HRT has been a common treatment for some of the symptoms experienced during menopause, although rates dropped greatly after a 2002 study linked the practice to increased risks for breast cancer, stroke and heart disease. When estrogen is used alone (estrogen replacement therapy [ERT]), the breast cancer risk appears to be lower than with combination HRT including progesterone.
- Breast density. Women with less fatty, denser breasts, which are normally older women, have an increased chance of breast cancer.
- Exposure to DES (diethylstilbestrol). A synthetic estrogen widely prescribed from the early 1940s through the early 1970s for pregnant women, DES is believed to slightly increase a woman’s risk of breast cancer. For years, DES was also linked to rare vaginal and cervical cancers in the daughters exposed to the drug during their mothers’ pregnancies.
New research shows that these DES daughters also have an increased risk of developing breast cancer. - Obesity after menopause. In postmenopausal women, estrogen is primarily produced by fat tissue. If a woman is significantly overweight, she has more fat tissue and more estrogen is being produced in their body. In a recent study conducted by the ACS, women who were overweight based on a body mass index (BMI) greater than 25 are 1.3 to 2.1 times more likely to die from breast cancer than women with a normal BMI. Women who are obese prior to menopause do not demonstrate the same increased risk.
- Radiation to the chest area. For women treated for Hodgkin’s lymphoma with radiation to the chest before age 30, the chances of developing breast cancer are higher than the general population.
- Sedentary lifestyle. Women who are physically inactive have a higher rate of breast cancer, possibly due to a sedentary lifestyle leading to a person becoming overweight or obese, which is also an independent risk factor for breast cancer.
- Use of alcohol. Several studies have concluded that the more alcohol consumed by a woman, the higher her risk of breast cancer becomes. Analysis of these studies suggests that the equivalent of two alcoholic drinks per day may increase the risk of breast cancer by 21 percent. The risk is thought to be related to alcohol causing an increase in the body's hormone levels.
- Smoking. Smoking significantly increases the risk of developing this disease, particularly for those with a family history of breast cancer.
Although the specific causes of breast cancer are unknown, some associations are becoming clearer. The effect of hormones on tumors and development is apparent, as are changes in the DNA of numerous genes.
