By now you may be familiar with the statistic that says 1 in 8 women will develop invasive breast cancer. Many people misinterpret this to mean that, on any given day, they and the women they know have a 1-in-8 risk of developing the disease. That?s simply not true.
In reality, about 1 in 8 women in the United States ? 12%, or about 12 out of every 100 ? can expect to develop breast cancer over the course of an entire lifetime. In the U.S., an average lifetime is about 80 years. So, it?s more accurate to say that 1 in 8 women in the U.S. who reach the age of 80 can expect to develop breast cancer. In each decade of life, the risk of getting breast cancer is actually lower than 12% for most women.
People tend to have very different ways of viewing risk. For you, a 1-in-8 lifetime risk may seem like a high likelihood of getting breast cancer. Or you may turn this around and reason that there is a 7-in-8, or 87.5%, chance you will never get breast cancer, even if you live to age 80. How you view risk often depends on your individual situation ? for example, whether you or many women you know have had breast cancer, or you have reason to believe you are at higher-than-normal risk for the disease ? and your usual way of looking at the world.
Even though studies have found that women have a 12% lifetime risk of developing breast cancer, your individual risk may be higher or lower than that. Individual risk is affected by many different factors, such as family history, reproductive history, lifestyle, environment, and others.
For more information on understanding breast cancer risk and risk factors, visit the Lower Your Risk section of Breastcancer.org.
Absolute risk is used to describe an individual?s likelihood of developing breast cancer. It is based on the number of people who will develop breast cancer within a certain time period. Absolute risk also can be stated as a percentage.
When we say that 1 in 8 women in the United States, or 12%, will develop breast cancer over the course of a lifetime, we are talking about absolute risk. On average, an individual woman has a 1-in-8 chance of developing breast cancer over an 80-year lifespan.
The absolute risk of developing breast cancer during a particular decade of life is lower than 1 in 8. The younger you are, the lower the risk. For example:
- From age 30 to 39, absolute risk is 1 in 233, or 0.43%. This means that 1 in 233 women in this age group can expect to develop breast cancer. Put another way, your odds of developing breast cancer if you are in this age range are 1 in 233.
- From age 40 to 49, absolute risk is 1 in 69, or 1.4%.
- From age 50 to 59, absolute risk is 1 in 38, or 2.6%.
- From age 60 to 69, absolute risk is 1 in 27, or 3.7%.
As you can see, the older you are, the higher your absolute risk of breast cancer. Keep in mind that these numbers and percentages are averages for the whole population. Your individual breast cancer risk may be higher or lower, depending on a number of factors, including family history, reproductive history (such as menstrual and childbearing history), race/ethnicity, and other factors.
Take family history, for example. The absolute risk of breast cancer is much higher for women who have inherited mutations in the genes known as BRCA1 or BRCA2. Their absolute risk over the course of a lifetime ranges from 40-85%. This means that out of every 100 women who have these mutations, anywhere from 40 to 85 of them can expect to develop breast cancer should they live to age 80.
If you have breast cancer, absolute risk also can be used to describe the likelihood of a certain treatment outcome or the course of the disease. For example, suppose that, based on the characteristics of the breast cancer (stage, grade, other test results), your age and medical history, and the treatments you have, your doctor tells you that your likelihood of disease-free survival at 5 years ? being alive with no evidence of breast cancer ? is 90%. This means that your absolute risk of having the breast cancer come back within 5 years is 10%, or 1 in 10. In other words, 1 out of 10 women with similar characteristics and the same treatment plan can expect to have a recurrence within that time frame. Nine out of 10, or 90%, would not.
Relative risk is a number or percentage that compares one group?s risk of developing breast cancer to another?s. This is the type of risk frequently reported by research studies, which often compare groups of women with different characteristics or behaviors to determine whether one group has a higher or lower risk of breast cancer than the other (either as a first-time diagnosis or recurrence).
Understanding relative risk can help you answer an important question: If I make certain lifestyle choices or have certain treatments, how much will I increase or decrease my risk of developing breast cancer or having a recurrence?
Example of breast cancer risk going up
Many studies have shown that women who have two or more alcoholic drinks each day have a higher risk of developing breast cancer. (A drink is defined as 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of 80-proof liquor.) You may hear this relative risk described as a percentage or a number:
- Compared to women who do not drink, women who have two or more drinks per day have a 25% higher risk of breast cancer. Put another way, they are 25% more likely to develop breast cancer over the course of a lifetime than nondrinkers are. This doesn?t mean that their lifetime risk of getting breast cancer is 25% ? it means that their risk of getting breast cancer is 25% higher relative to people who don?t drink. This percentage is how you are likely to see relative risk reported by television, the Internet, and newspapers.
- Compared to women who do not drink, women who have two or more drinks per day have a relative risk of 1.25. This number is how researchers and scientific papers would usually talk about relative risk. The number ?1? is assigned to the baseline group (women who do not drink), since their risk remains the same. The .25 describes the relative increase in risk for the other group; it is another way of expressing the 25% higher lifetime risk (25% = .25).
Another way of saying this is that women who drink two or more alcoholic drinks per day have 1.25 (1 + .25 = 1.25) times the risk of developing breast cancer than women who do not drink.
Relative risk can be a tricky concept, because most people tend to focus on the reported percentage ? e.g., 25% higher risk ? which sounds alarming. Yes, a 25% higher risk of developing breast cancer (relative to people who don?t drink) is significant, but it doesn?t tell a woman what her lifetime risk is if she drinks two or more alcoholic drinks per day for the rest of her life. Since women in this group have 1.25 times the risk of developing breast cancer, it?s necessary to multiply the absolute risk of breast cancer (12%) for women in the general population (13%, or .13) by relative risk (1.25):
- .127 x 1.25 = .159. This means that a woman?s absolute lifetime risk of developing breast cancer if she drinks two or more alcoholic drinks per day is just under 16%, versus 12% for women who do not drink.
Many different factors can increase and/or decrease your risk of developing breast cancer. Online tools such as the National Cancer Institute?s Breast Cancer Risk Assessment Tool allow you to input individual information to calculate your risk.
Example of breast cancer risk going down
Suppose you have had breast cancer and undergone lumpectomy (removal of the tumor itself and a margin of healthy surrounding tissue). The absolute risk of the breast cancer coming back in the same breast is about 25%. But if you have radiation therapy to the remaining breast tissue, you can reduce that risk by about 60%. To describe this relative risk decrease, your doctor might say:
- Compared to women who have lumpectomy alone, you have a 60% lower risk of developing breast cancer again in the same breast if you have radiation therapy after lumpectomy.
Medical researchers might express it this way:
- Compared to women who do not have radiation therapy, your relative risk of developing breast cancer is .40 (1 ? .60 = .40). Again, the number ?1? is assigned to the baseline group, which is not taking the extra action to decrease the risk. The .60 is subtracted from 1 because it represents a decrease in risk. In other words, you have about 40% of the risk of developing breast cancer again in the same breast as they do.
So in this scenario, what difference does radiation therapy really make for you in terms of reducing the absolute risk of cancer recurrence in the same breast? To know that, you have to multiply the risk of recurrence without radiation (25%, or .25) by the relative risk of .40:
- .25 X .40 =.10. In this hypothetical situation, your absolute risk of the cancer returning in the same breast is 10%, or 1 in 10, if you have radiation therapy, versus about 25%, or 1 in 4, if you don?t. Put another way, 1 in 10 women who have radiation therapy can expect to experience recurrence in the same breast, versus 1 in 4 women who do not have the treatment.
So, relative risk is the number that tells you how much something you do, such as a certain behavior or treatment, can change your risk for breast cancer compared to those who don?t do it. A relative risk of:
- .5 means that your risk decreases by half, or 50%
- 1.88 means that your risk increases by 88%
- 3.0 means that your risk triples, or goes up by 300% (you have three times the risk)
As the examples above show, knowing how much your breast cancer risk goes up or down with certain lifestyle factors and treatment options can help you and your doctor make the best decisions for you. These are hypothetical examples; you can find out more about breast cancer risk in the Lower Your Risk section.
A ?risk factor? is anything that increases your risk of developing breast cancer. Many of the most important risk factors for breast cancer are beyond your control, such as age, family history, and medical history. However, there are some risk factors you can control, such as weight, physical activity, and alcohol consumption.
Be sure to talk with your doctor about all of your possible risk factors for breast cancer. There may be steps you can take to lower your risk of breast cancer, and your doctor can help you come up with a plan. Your doctor also needs to be aware of any other risk factors beyond your control, so that he or she has an accurate understanding of your level of breast cancer risk. This can influence recommendations about breast cancer screening ? what tests to have and when to start having them.
Risk factors you can control
Weight. Being overweight is associated with increased risk of breast cancer, especially for women after menopause. Fat tissue is the body?s main source of estrogen after menopause, when the ovaries stop producing the hormone. Having more fat tissue means having higher estrogen levels, which can increase breast cancer risk.
Diet. Diet is a suspected risk factor for many types of cancer, including breast cancer, but studies have yet to show for sure which types of foods increase risk. It?s a good idea to restrict sources of red meat and other animal fats (including dairy fat in cheese, milk, and ice cream), because they may contain hormones, other growth factors, antibiotics, and pesticides. Some researchers believe that eating too much cholesterol and other fats are risk factors for cancer, and studies show that eating a lot of red and/or processed meats is associated with a higher risk of breast cancer. A low-fat diet rich in fruits and vegetables is generally recommended. For more information, visit our page on healthy eating to reduce cancer risk in the Nutrition section.
Exercise. Evidence is growing that exercise can reduce breast cancer risk. The American Cancer Society recommends engaging in 45-60 minutes of physical exercise 5 or more days a week.
Alcohol consumption. Studies have shown that breast cancer risk increases with the amount of alcohol a woman drinks. Alcohol can limit your liver?s ability to control blood levels of the hormone estrogen, which in turn can increase risk.
Smoking. Smoking is associated with a small increase in breast cancer risk.
Exposure to estrogen. Because the female hormone estrogen stimulates breast cell growth, exposure to estrogen over long periods of time, without any breaks, can increase the risk of breast cancer. Some of these risk factors are under your control, such as:
- taking combined hormone replacement therapy (estrogen and progesterone; HRT) for several years or more, or taking estrogen alone for more than 10 years
- being overweight
- regularly drinking alcohol
Recent oral contraceptive use. Using oral contraceptives (birth control pills) appears to slightly increase a woman?s risk for breast cancer, but only for a limited period of time. Women who stopped using oral contraceptives more than 10 years ago do not appear to have any increased breast cancer risk.
Stress and anxiety. There is no clear proof that stress and anxiety can increase breast cancer risk. However, anything you can do to reduce your stress and to enhance your comfort, joy, and satisfaction can have a major effect on your quality of life. So-called ?mindful measures? (such as meditation, yoga, visualization exercises, and prayer) may be valuable additions to your daily or weekly routine. Some research suggests that these practices can strengthen the immune system.
Risk factors you can?t control
Gender. Being a woman is the most significant risk factor for developing breast cancer. Although men can get breast cancer, too, women?s breast cells are constantly changing and growing, mainly due to the activity of the female hormones estrogen and progesterone. This activity puts them at much greater risk for breast cancer.
Age. Simply growing older is the second biggest risk factor for breast cancer. From age 30 to 39, the risk is 1 in 233, or .43%. That jumps to 1 in 27, or almost 4%, by the time you are in your 60s.
Family history of breast cancer. If you have a first-degree relative (mother, daughter, sister) who has had breast cancer, or you have multiple relatives affected by breast or ovarian cancer (especially before they turned age 50), you could be at higher risk of getting breast cancer.
Personal history of breast cancer. If you have already been diagnosed with breast cancer, your risk of developing it again, either in the same breast or the other breast, is higher than if you never had the disease.
Race. White women are slightly more likely to develop breast cancer than are African American women. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.
Radiation therapy to the chest. Having radiation therapy to the chest area as a child or young adult as treatment for another cancer significantly increases breast cancer risk. The increase in risk seems to be highest if the radiation was given while the breasts were still developing (during the teen years).
Breast cellular changes. Unusual changes in breast cells found during a breast biopsy (removal of suspicious tissue for examination under a microscope) can be a risk factor for developing breast cancer. These changes include overgrowth of cells (called hyperplasia) or abnormal (atypical) appearance.
Exposure to estrogen. Because the female hormone estrogen stimulates breast cell growth, exposure to estrogen over long periods of time, without any breaks, can increase the risk of breast cancer. Some of these risk factors are not under your control, such as:
- starting menstruation (monthly periods) at a young age (before age 12)
- going through menopause (end of monthly cycles) at a late age (after 55)
- exposure to estrogens in the environment (such as hormones in meat or pesticides such as DDT, which produce estrogen-like substances when broken down by the body)
Pregnancy and breastfeeding. Pregnancy and breastfeeding reduce the overall number of menstrual cycles in a woman?s lifetime, and this appears to reduce future breast cancer risk. Women who have never had a full-term pregnancy, or had their first full-term pregnancy after age 30, have an increased risk of breast cancer. For women who do have children, breastfeeding may slightly lower their breast cancer risk, especially if they continue breastfeeding for 1 1/2 to 2 years. For many women, however, breastfeeding for this long is neither possible nor practical.
DES exposure. Women who took a medication called diethylstilbestrol (DES), used to prevent miscarriage from the 1940s through the 1960s, have a slightly increased risk of breast cancer. Women whose mothers took DES during pregnancy may have a higher risk of breast cancer as well.