Breast Cancer Risk and Prevention
It is one of the most common cancers in women. You often hear the statistic of 1 in 8 women developing breast cancer in their lifetime, but what does that really mean? You can think of it as a 12% lifetime risk, so 12 out of 100 women will get the disease in their lifetime – which means the other 88 women will not. Men are also at risk of breast cancer, although this risk is much lower than it is for women and we will not discuss male risk in this article.
Many factors play into your risk of developing breast cancer. These include family history, reproductive history, diet, alcohol use, weight, hormone use, and radiation exposure. As you can see, some risk factors are modifiable, meaning you can change them (i.e. diet, alcohol use). Others are nonmodifiable, such as family history or early menarche (start of menstruation). This article will review what puts you at risk for developing breast cancer, and for the modifiable factors, provide resources to make changes to reduce risk.
Risk factors can increase the chance of developing a cancer, but they do not mean that you are certain to develop the cancer. It is also important to point out that about 70% of the women who develop breast cancer do not have any of these risk factors and more than 85% have no family history of the disease. Because of this fact, all women should discuss screening for breast cancer with their providers.
The most important risk factor for the development of breast cancer is increasing age. The risk of breast cancer is higher as you get older - more women get breast cancer in their 60s and 70s than in their 30s or 40s. The risk increases gradually as a woman ages.
Women's Health History
Certain pieces of a woman's health history can increase breast cancer risk. For most women, these are not factors that you can change, but you may want to know about them.
Women who have their first menstrual period before age 12 or go through menopause later (after age 55) have a slightly higher risk of breast cancer. This is thought to be because they will have a longer lifetime exposure to estrogen in their bodies. Along the same lines, some studies have suggested that breastfeeding can slightly reduce risk. This may also be related to the number of menstrual periods and estrogen exposure.
The age of the woman at her first live birth of a child can affect risk, but the effect varies depending on the number of first-degree relatives who have been diagnosed with breast cancer. For women with 2 or more 1st-degree relatives (i.e. mother, sister) with a diagnosis, their risk decreased with an older age at first live birth. For women with no family history, risk increases with older age at first live birth.
There is an increase in risk for women who have had a breast biopsy in the past. Two biopsy results have a stronger affect on risk. Atypical hyperplasia is not a cancer, but increases the risk of developing a breast cancer by 3-5 times that of a woman without this history. Lobular carcinoma in situ (LCIS) are cancer cells that are confined to the lobules in the breast tissue. LCIS is not treated like other breast cancers, but results in careful monitoring and may result in taking medications to reduce future risk. The presence of LCIS means your risk of developing breast cancer is 7 to 11 times higher than an average woman.
Women who have had a biopsy showing atypical hyperplasia or LCIS should have annual screening with mammography and breast exams by a healthcare provider 1-2 times a year. Some women may also have MRIs for screening and may be eligible for drug therapy (tamoxifen or raloxifine) to decrease the chance of developing breast cancer and/or to participate in a clinical trial for this condition. You should discuss these options with your provider.
Researchers have created a program, called the Breast Cancer Risk Assessment Tool, that takes many of these women's health factors into consideration and calculates an estimated risk of developing breast cancer in the next 5 years and in the woman's lifetime. These calculations are based on the Gail Model, a statistical model for determining risk. Learn more about the Model or use the tool.
Hormone Replacement Therapy
Hormone replacement therapy (HRT) was often prescribed for menopausal women to reduce hot flashes, vaginal dryness, and risk of bone fractures and heart disease. In July 2002, a large study found that HRT was doing more harm than good and changed healthcare providers' practice almost overnight. The Women's Health Initiative (WHI) found that taking HRT (estrogen combined with progestin) resulted in an increased risk of breast cancer, heart disease, stroke, and blood clots. While there was the benefit of reduction in bone fractures related to osteoporosis and fewer colorectal cancer cases, the risks far outweighed these benefits. Around the same time, the HERS study found that taking HRT resulted in no decrease in heart attacks in older women with heart disease. A few years later, the WHI study also found that taking estrogen alone (for women without a uterus) resulted in increased risk for stroke and blood clots and no improvement in heart disease.
A follow-up study confirmed that women who take HRT for longer than 5 years, double their annual risk of breast cancer. The study did find that after stopping HRT, the risk decreases significantly.
Healthcare providers now recommend that women take HRT only when absolutely necessary to control menopausal symptoms in the lowest possible doses, for the shortest time possible. The WHI is continuing to follow the participants to determine any long term risks related to HRT.
What can you do if you took HRT in the past? Be sure your healthcare providers know that you took HRT, and for how long. You can periodically check on the WHI website to learn about study updates.
Birth Control Pills & Cancer Risk
Birth control pills (BCPs) were first introduced in the 1960s and are the most commonly used method of contraception in the United States. Since they have first started being used, the components and doses of BCPs have changed. For instance, early BCPs contained 150 micrograms of ethinyl estradiol, whereas today's BCPs contain an average of 20 micrograms. These changes make it hard to apply the results of previous studies examining cancer risk to today's BCP preparations.
In 2005, the International Agency for Research on Cancer released a report calling BCPs carcinogenic (cancer-causing); however, many of the studies used in this analysis were looking at older, higher-dose formulations of BCPs. They found a small increased risk of breast cancer for current users and for 9 years after users stopped BCPs, after which there was no increased risk. They also found that BCPs decreased the risk of endometrial and ovarian cancer and possibly colon cancer. More recent studies of modern BCP doses have found no increase in breast cancer risk among current or former users. It is not known whether the newer formulations provide the same protective effect for endometrial and ovarian cancers.
Recent studies have not found a higher risk of breast cancer in women with a strong family history or carriers of genetic mutations (BRCA1/2) who take or have taken BCPs. There are no recommendations for any increased screening for women who have taken birth control pills.
Learn more from the National Cancer Institute.
Family History of Breast Cancer
How your family members' diagnoses affect your risk partly depends on how closely related you are and at what age the woman or women in your family were diagnosed. If you have a first-degree relative (sister, mother, daughter) with a breast cancer diagnosis, your risk is double that of someone without a family history. Having 2 first-degree relatives with the disease increases risk about 3-fold. If your father or brother has had male breast cancer, your risk is also increased, though to what degree is not clear. If you are someone with a first-degree relative(s) with the disease, you may need to begin screening mammograms at an earlier age then the ACS guidelines of 40. Discuss this history with your healthcare providers to determine if there are any red flags for hereditary cancer syndromes, which warrant a discussion with a genetic counselor and possibly genetic testing.
But what about most women, who have a more distant relative(s) with the disease? This is where things become less certain. If the family history has several people diagnosed with the same cancer or diagnoses before age 50, discussion with a genetic counselor is warranted. If not, the evidence for increased risk is less convincing and standard screening is typically recommended (mammogram annually, beginning at age 40). As with any family history, be sure to discuss your situation with your healthcare providers.
Personal History of Breast Cancer
If you have had breast cancer in the past, you are 3 to 4 times more likely to develop another breast cancer compared to a woman who has never had the disease - not metastases or spread from the first cancer, but a new cancer altogether. This may occur in the same breast or the other breast. This is why it is so important to keep follow up appointments with your oncology team and continue recommended screening tests.
It is estimated that 5-10% of breast cancers are hereditary, meaning they are the result of a faulty gene that was inherited from a parent. BRCA 1 & 2 are the most common and well-understood mutations, but they are not the only genetic mutations that can increase breast cancer risk. Women should consider discussing their case with a genetic counselor if they are concerned about their family history. Guidelines recommend that a woman be screened if any of the following apply:
- Multiple family members have been diagnosed with breast or ovarian cancer, particularly if the diagnoses came before age 50.
- Family members who have had bilateral breast cancer (in both breasts).
- Both breast and ovarian cancer is present in the family.
- There are any cases of male breast cancer in the family.
- In addition to breast cancer, family members on the same side of the family have had prostate cancer (at a young age), colorectal cancers, stomach cancer, pancreatic cancer, and endometrial cancer.
- Families of Ashkenazi Jewish heritage.
BRCA1/BRCA2 Genetic Predisposition
The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 or BRCA2 gene. If you have inherited a mutated copy of either gene from a parent, you have an estimated 40-85% chance of developing breast cancer during your lifetime. People with these mutations tend to develop cancer at a younger age (before age 40) and these cancers more often affect both breasts. People with these inherited mutations also have an increased risk for developing other cancers, particularly ovarian cancer, but also male breast cancer, pancreatic cancer, and prostate cancer. BRCA mutations occur more commonly in individuals of Ashkenazi Jewish (Eastern European) descent, as well as Norwegian, Dutch, and Icelandic populations, but they can occur in any racial or ethnic group.
If you know that you have a BRCA 1 or BRCA2 mutation, you should talk to a healthcare provider to ensure you receive the proper screening or treatment (chemoprevention) to reduce the chance of developing cancer or to detect cancer at an earlier stage when treatment is most effective. Your healthcare provider may recommend getting mammograms at a younger age, special breast and/or ovarian cancer screening tests, or other interventions, such as, prophylactic (preventative) surgery or chemoprevention.
DES Exposure for Mothers & Daughters
DES was the first synthetic estrogen and was given to pregnant women from 1938-1971 because it was believed to prevent miscarriages and promote "healthy pregnancies." It was found that not only did the drug not prevent problems associated with pregnancy, it also caused health issues for the women taking it, as well as children born of these pregnancies. Women who took DES and their daughters have been found to be at higher risk of developing breast cancer.
Learn more about this risk and recommendations for screening.
Previous Chest Radiation
Women who had radiation therapy to the chest area as treatment for another cancer (i.e. Hodgkin disease) have a significantly increased risk for breast cancer. The exact risk varies depending on the age at which they were treated. Risk is highest for those treated as adolescents, while breast tissue was in development. Treatment after age 40 does not seem to increase breast cancer risk. For Hodgkin's disease survivors who had radiation to the chest or axilla (armpit area), recommendations can include:
- Annual breast exam by a healthcare professional, and monthly self-breast exam.
- Begin annual mammograms 8-10 years post-therapy.
- Breast MRI, in addition to the annual mammogram.
Speak to your provider about when you should start mammograms and breast MRI as screening.
Alcohol Use and Breast Cancer Risk
Many people are aware that heavy alcohol use can cause health problems such as cirrhosis of the liver, hepatitis, high blood pressure, heart disease, and stroke, but many are not aware that alcohol can also increase your risk of developing several types of cancer, including breast cancer. Alcohol appears to increase the levels of estrogen in the body and can increase the risk of hormone positive breast cancer (also called ER+ or PR+).
Heavy drinkers have 10-15 times higher risk of developing a cancer than those who do not drink. However, the overall risk increases after just 1 drink a day for women or 2 for men. (A drink is defined as 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of 80-proof liquor.) Higher breast cancer risk has been associated with just 3 drinks a week, so the risk is not limited to heavy drinking. Women who have 2 alcoholic drinks a day are 1.5 times more likely to develop breast cancer than a woman who never drank alcohol.
Learn more about how alcohol causes cancer and resources for quitting at the American Cancer Society.
Breast Cancer Risk Reduction
The Prevention Triangle: Diet, Activity & Healthy Weight
While the media often reports on foods that "prevent cancer" and we would love to be told that eating one particular food would prevent cancer, it is unlikely that such a food exists. It is more likely that a combination of good foods may have a preventive effect. Studies over the years have looked at our diets and what foods, if any, will lead to a lower risk of cancer. Fruits and vegetables, whole grains and unprocessed foods have all been promoted as reducing cancer risk. Unfortunately, studies have not consistently proven this to be true. Expert panels state that a diet high in fruits and vegetables "probably" reduces cancer risk, but we just don't know for sure.
However, a healthy diet plays an important role in a sort of "triangle" of cancer prevention. A healthy diet, combined with regular physical activity and maintaining a healthy weight has been shown to reduce cancer risk. This triangle is thought to be the second most important step, after not smoking, to preventing any type of cancer. Being overweight and having a diet high in fat is clearly related to the development of breast cancer. In addition, research has shown that being overweight increases the risk that a woman who has had breast cancer is much more likely to have that cancer recur.
Learn more about how the prevention triangle can help to prevent breast cancer.
Chemoprevention – Preventing the Development of Breast Cancer with Medications
Tamoxifen was the first chemoprevention medicine to receive FDA approval and is the most well-known and studied chemoprevention agent. The Breast Cancer Prevention Trial, showed that tamoxifen reduces a pre-or post-menopausal high-risk woman's chances of developing breast cancer by as much as one-half.
Tamoxifen only affects tumors that are estrogen receptor positive (ER+); there is no effect on tumors that are estrogen receptor negative (ER-). Side effects of tamoxifen include increased risk of endometrial cancer and blood clot formation. It can also increase the risk for osteoporosis in pre-menopausal women.
Raloxifene is another SERM that can prevent breast cancer in postmenopausal women. This medication is also used to prevent and treat osteoporosis. Raloxifene also works by blocking estrogen's effects in the breast and other tissues, but appears to have fewer risks, compared to tamoxifen. Unlike tamoxifen, raloxifene doesn't exert estrogen-like effects on the uterus, so there is no increased risk of endometrial cancer.
The National Surgical Adjuvant Breast and Bowel Project studied both tamoxifen and raloxifene for breast cancer chemoprevention in the STAR trial. Women were assigned to take either tamoxifen or raloxifene daily for five years. The results showed that tamoxifen and raloxifene both reduced the risk of invasive breast cancer in high-risk women by about 50%.
Aromatase inhibitor medications are being studied for chemoprevention. Studies of women who took these medications as a treatment for breast cancer found that they were less likely to develop another cancer. Neither raloxifene or aromatase inhibitors were studied in women with BRCA 1 or 2 genes, so it is not clear how well they work in these women.
The decision to use a chemopreventive agent very personal and should include a detailed discussion between the patient and their healthcare provider about the risks and benefits of this therapy.
Risk for breast cancer and screening recommendations will depend on your personal history and goals. Speak with your provider about your personal risk and your options for screening.
American Cancer Society. Deciding Whether to Use Medicine to Reduce Breast Cancer Risk. 2019.
FORCE. Breast Cancer Chemoprevention. 2019.
BreastCancer.org. Breast Cancer Risk Factors.