Do you ever wonder how likely you are to be diagnosed with breast cancer? Unfortunately, breast cancer is very common. The average woman in the United States has about a 12%, or 1 in 8, chance of being diagnosed with breast cancer during her lifetime.
The vast majority of breast cancer risk factors are related to greater exposure to estrogen, so women who started having menstrual cycles early, go through menopause at an older age and take hormones after menopause are at a mildly higher risk. Obesity is an important risk factor, especially after menopause. Fatty tissue in our bodies actually creates estrogen-like compounds, so being overweight increases the risk of breast cancer. Drinking alcohol can affect the liver where estrogen is processed; even one glass a day can increase the risk of breast cancer. On the other hand, pregnancy and breastfeeding are somewhat protective. Each of these estrogen-related risk factors has only a small impact on breast cancer risk. None of the estrogen-related risk factors alone will make a woman high risk, but when added together, they can be more significant. These factors are likely why breast cancer is more common for women in developed countries like the United States, where periods tend to start at a younger age, childbirth is delayed, obesity and alcohol use are common and hormone use is more frequent.
Characteristics of the breast tissue itself can also increase the risk of cancer. Women with very dense breast tissue (this appears white on the mammogram) are more likely to develop breast cancer than women whose breasts are more fatty. Dense tissue can also hide cancer on a mammogram. While women with dense breast tissue should definitely get mammograms every year, they should also think about having extra testing, such as an ultrasound. Women who have had more breast biopsies, and especially if these showed any abnormal cells (also called atypia), are also at higher risk than average women. Likewise, women who undergo high-dose radiation for treatment of chest disease at a young age, such as Hodgkins Lymphoma, are at higher risk for breast cancer.
A very small number of women (~1% of the population) are at extremely high risk (60-80% chance of having breast cancer during their lifetime) because of a genetic mutation that is inherited from one of their parents. These are the “BRCA” or Breast Cancer genes. Women with a strong family history of breast or ovarian cancer on either mom or dad’s side of the family may carry one of these genetic mutations. Genetic counseling and testing are helpful when a gene mutation is suspected. These genes are more common in families of Ashkenazi Jewish heritage. Women who are at very high risk for breast cancer should have an MRI for screening in addition to mammography. They may also try other ways to reduce their risk of breast cancer.
There are some things that you might think would increase the risk of breast cancer, but actually do not. Exposure to low-dose radiation from mammography (well regulated by the FDA) does not have a significant impact on breast cancer risk compared with the benefit of early detection. Tobacco use, although terrible for health in so many ways, does not increase the risk of breast cancer. Women having breast surgery have been told to avoid deodorant, as this can cause problems if the lymph nodes under the arm have been removed, but deodorant does not increase the risk of breast cancer. Modern day birth control pills are lower in dose than our own hormone levels and so do not increase risk of breast cancer.
Bottom line – breast cancer is common, and most of us have many small risk factors that make us susceptible to this disease. Mammography is currently our best defense in the fight to reduce our chance of dying of this disease. Women with a strong family history of breast or ovarian cancer, families with known or suspected genetic mutations (like BRCA) that increase risk of disease, women with prior high-dose radiation to the chest to treat other cancers at a young age and women with prior breast biopsies showing abnormal cells are at very high risk and should seek professional risk assessment and counseling.
Dr. Jennifer A. Harvey is a Professor of Radiology and Medical Imaging; Co-Director, UVA Breast Care Program; Division Director, Breast Imaging