Breast Cancer Awareness Month
Breast cancers can start from different parts of the breast.
- Most breast cancers begin in the ducts that carry milk to the nipple (ductal cancers)
- Some start in the glands that make breast milk (lobular cancers)
- There are also other types of breast cancer that are less common like phyllodes tumor and angiosarcoma
- A small number of cancers start in other tissues in the breast. These cancers are called sarcomas and lymphomas and are not really thought of as breast cancers.
Although many types of breast cancer can cause a lump in the breast, not all do. See Breast Cancer Signs and Symptoms to learn what you should watch for and report to a health care provider. Many breast cancers are also found on screening mammograms, which can detect cancers at an earlier stage, often before they can be felt, and before symptoms develop.
How breast cancer spreads
Breast cancer can spread when the cancer cells get into the blood or lymph system and are carried to other parts of the body.
The lymph system is a network of lymph (or lymphatic) vessels found throughout the body that connects lymph nodes (small bean-shaped collections of immune system cells). The clear fluid inside the lymph vessels, called lymph, contains tissue by-products and waste material, as well as immune system cells. The lymph vessels carry lymph fluid away from the breast. In the case of breast cancer, cancer cells can enter those lymph vessels and start to grow in lymph nodes. Most of the lymph vessels of the breast drain into:
- Lymph nodes under the arm (axillary nodes)
- Lymph nodes around the collar bone (supraclavicular [above the collar bone] and infraclavicular [below the collar bone] lymph nodes)
- Lymph nodes inside the chest near the breast bone (internal mammary lymph nodes)
Lifestyle-related Breast Cancer Risk Factors
A risk factor is anything that increases your chances of getting a disease, such as breast cancer. But having a risk factor, or even many, does not mean that you are sure to get the disease.
Certain breast cancer risk factors are related to personal behaviors, such as diet and exercise. Other lifestyle-related risk factors include decisions about having children and taking medicines that contain hormones.
For information on other known and possible breast cancer risk factors, see:
- Breast Cancer Risk Factors You Cannot Change
- Factors with Unclear Effects on Breast Cancer Risk
- Disproven or Controversial Breast Cancer Risk Factors
Drinking alcohol is clearly linked to an increased risk of breast cancer. The risk increases with the amount of alcohol consumed. Women who have 1 alcoholic drink a day have a small (about 7% to 10%) increase in risk compared with non-drinkers, while women who have 2 to 3 drinks a day have about a 20% higher risk than non-drinkers. Alcohol is linked to an increased risk of other types of cancer, too.
Being overweight or obese
Being overweight or obese after menopause increases breast cancer risk. Before menopause your ovaries make most of your estrogen, and fat tissue makes only a small part of the total amount. After menopause (when the ovaries stop making estrogen), most of a woman’s estrogen comes from fat tissue. Having more fat tissue after menopause can raise estrogen levels and increase your chance of getting breast cancer. Also, women who are overweight tend to have higher blood insulin levels. Higher insulin levels have been linked to some cancers, including breast cancer.
Still, the link between weight and breast cancer risk is complex.
For instance, the risk of breast cancer after menopause is higher for women who gained weight as an adult, but the risk before menopause is actually lower in women who are obese. The reasons for this aren’t exactly clear.
Weight might also have different effects on different types of breast cancer. For example, being overweight after menopause is more strongly linked with an increased risk of hormone receptor-positive breast cancer, whereas some research suggests that being overweight before menopause might increase your risk of the less common triple-negative breast cancer.
The American Cancer Society recommends you stay at a healthy weight throughout your life and avoid excess weight gain by balancing your food intake with physical activity.
Not being physically active
Evidence is growing that regular physical activity reduces breast cancer risk, especially in women past menopause. The main question is how much activity is needed. Some studies have found that even as little as a couple of hours a week might be helpful, although more seems to be better.
Exactly how physical activity might reduce breast cancer risk isn’t clear, but it may be due to its effects on body weight, inflammation, hormones, and energy balance.
The American Cancer Society recommends that adults get 150 to 300 minutes of moderate intensity or 75 to 150 minutes of vigorous intensity activity each week (or a combination of these). Getting to or going over the upper limit of 300 minutes is ideal.
Not having children
Women who have not had children or who had their first child after age 30 have a slightly higher breast cancer risk overall. Having many pregnancies and becoming pregnant at an early age reduces breast cancer risk.
Still, the effect of pregnancy on breast cancer risk is complex. For example, the risk of breast cancer is higher for about the first decade after having a child, particularly for hormone receptor-negative breast cancer (including the less common triple-negative breast cancer). The risk then becomes lower over time.
Most studies suggest that breastfeeding may slightly lower breast cancer risk, especially if it’s continued for a year or more. But this has been hard to study, especially in countries like the United States, where breastfeeding for this long is uncommon.
The explanation for this possible effect may be that breastfeeding reduces a woman’s total number of lifetime menstrual cycles (the same as starting menstrual periods at a later age or going through early menopause).
Some birth control methods use hormones, which might increase breast cancer risk.
Oral contraceptives: Most studies have found that women using oral contraceptives (birth control pills) have a slightly higher risk of breast cancer than women who have never used them. Once the pills are stopped, this risk seems to go back to normal within about 10 years.
Birth control shot: Depo-Provera is an injectable form of progesterone that’s given once every 3 months for birth control. Some studies have found that women currently using birth-control shots seem to have an increase in breast cancer risk, but other studies have not found an increased risk.
Birth control implants, intrauterine devices (IUDs), skin patches, vaginal rings: These forms of birth control also use hormones, which in theory could fuel breast cancer growth. Some studies have shown a link between use of hormone-releasing IUDs and breast cancer risk, but few studies have looked at the use of birth control implants, patches, and rings and breast cancer risk.
Hormone therapy after menopause
Hormone therapy with estrogen (often combined with progesterone) has been used for many years to help relieve symptoms of menopause and help prevent osteoporosis (thinning of the bones). This treatment goes by many names, such as post-menopausal hormone therapy (PHT), hormone replacement therapy (HRT), and menopausal hormone therapy (MHT).
There are 2 main types of hormone therapy. For women who still have a uterus (womb), doctors generally prescribe estrogen and progesterone (known as combined hormone therapy, or just HT). Progesterone is needed because estrogen alone can increase the risk of cancer of the uterus. For women who’ve had a hysterectomy (who no longer have a uterus), estrogen alone can be used. This is known as estrogen replacement therapy (ERT) or just estrogen therapy (ET).
Combined hormone therapy (HT): Use of combined hormone therapy after menopause increases the risk of breast cancer. This increase in risk is typically seen after about 4 years of use. Combined HT also increases the likelihood that the cancer may be found at a more advanced stage.
The increased risk from combined HT appears to apply mainly to current and recent users. A woman’s breast cancer risk seems to go back down within 5 years of stopping treatment.
Bioidentical hormone therapy: The word bioidentical is sometimes used to describe versions of estrogen and progesterone with the same chemical structure as those found naturally in people (as opposed to the slightly different versions found in most medicines). The use of these hormones has been marketed as a safe way to treat the symptoms of menopause. But because there aren’t many studies comparing “bioidentical” or “natural” hormones to synthetic versions of hormones, there’s no proof that they’re safer or more effective. More studies are needed to know for sure. Until then, the use of these bioidentical hormones should be considered to have the same health risks as any other type of hormone therapy.
Estrogen therapy (ET): Studies of the use of estrogen alone after menopause have had mixed results, with some finding a slightly higher risk and some finding no increase. If ET does increase the risk of breast cancer, it is not by much.
At this time there aren’t many strong reasons to use post-menopausal hormone therapy (either combined HT or ET), other than possibly for the short-term relief of menopausal symptoms. Along with the increased risk of breast cancer, combined HT also appears to increase the risk of heart disease, blood clots, and strokes. It does lower the risk of colorectal cancer and osteoporosis, but this must be weighed against the possible harms, especially since there are other ways to prevent and treat osteoporosis, and screening can sometimes prevent colon cancer. ET does not seem to increase breast cancer risk, but it does increase the risk of stroke.
The decision to use HT should be made by a woman and her doctor after weighing the possible risks and benefits (including the severity of her menopausal symptoms), and considering her other risk factors for heart disease, breast cancer, and osteoporosis. If they decide she should try HT for symptoms of menopause, it’s usually best to use it at the lowest dose that works for her and for as short a time as possible.
To learn more, see Menopausal Hormone Therapy and Cancer Risk.
Breast implants have not been linked with an increased risk of the most common types of breast cancer. However, they have been linked to a rare type of non-Hodgkin lymphoma called breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), which can form in the scar tissue around the implant. This lymphoma appears to happen more often in implants with textured (rough) surfaces rather than smooth surfaces. If BIA-ALCL does occur after an implant, it can show up as a lump, a collection of fluid, swelling, or pain near the implant, or as a change in a breast’s size or shape.
American Cancer Society screening recommendations for women at average breast cancer risk
These guidelines are for women at average risk for breast cancer. For screening purposes, a woman is considered to be at average risk if she doesn’t have a personal history of breast cancer, a strong family history of breast cancer, or a genetic mutation known to increase risk of breast cancer (such as in a BRCA gene), and has not had chest radiation therapy before the age of 30. (See below for guidelines for women at high risk.)
Women between 40 and 44 have the option to start screening with a mammogram every year.
Women 45 to 54 should get mammograms every year.
Women 55 and older can switch to a mammogram every other year, or they can choose to continue yearly mammograms. Screening should continue as long as a woman is in good health and is expected to live at least 10 more years.
All women should understand what to expect when getting a mammogram for breast cancer screening – what the test can and cannot do.
Clinical breast exams are not recommended for breast cancer screening among average-risk women at any age.
Mammograms are low-dose x-rays of the breast. Regular mammograms can help find breast cancer at an early stage, when treatment is most successful. A mammogram can often find breast changes that could be cancer years before physical symptoms develop. Results from many decades of research clearly show that women who have regular mammograms are more likely to have breast cancer found early, are less likely to need aggressive treatment like surgery to remove the breast (mastectomy) and chemotherapy, and are more likely to be cured.
Mammograms are not perfect. They miss some cancers. And sometimes a woman will need more tests to find out if something found on a mammogram is or is not cancer. There’s also a small possibility of being diagnosed with a cancer that never would have caused any problems had it not been found during screening. (This is called overdiagnosis.) It’s important that women getting mammograms know what to expect and understand the benefits and limitations of screening.
In recent years, a newer type of mammogram called digital breast tomosynthesis (commonly known as three-dimensional [3D] mammography) has become much more common, although it’s not available in all breast imaging centers.
Many studies have found that 3D mammography appears to lower the chance of being called back for follow-up testing. It also appears to find more breast cancers, and several studies have shown it can be helpful in women with more dense breasts. A large study is now in progress to better compare outcomes between 3D mammograms and standard (2D) mammograms.
It should be noted that 3D mammograms often cost more than 2D mammograms, and this added cost may not be covered by insurance.
The American Cancer Society breast cancer screening guidelines consider having had either a 2D or 3D mammogram as being in line with current screening recommendations. The ACS also believes that women should be able to choose between 2D and 3D mammography if they or their doctor believes one would be more appropriate, and that out-of-pocket costs should not be a barrier to having either one.
Clinical breast exam and breast self-exam
Research has not shown a clear benefit of regular physical breast exams done by either a health professional (clinical breast exams) or by women themselves (breast self-exams). There is very little evidence that these tests help find breast cancer early when women also get screening mammograms. Most often when breast cancer is detected because of symptoms (such as a lump), a woman discovers the symptom during usual activities such as bathing or dressing. Women should be familiar with how their breasts normally look and feel and should report any changes to a health care provider right away.
(While the American Cancer Society does not recommend regular clinical breast exams or breast self-exams as part of a routine breast cancer screening schedule, this does not mean that these exams should never be done. In some situations, particularly for women at higher than average risk, for example, health care providers may still offer clinical breast exams, along with providing counseling about risk and early detection. And some women might still be more comfortable doing regular self-exams as a way to keep track of how their breasts look and feel. But it’s important to understand that there is very little evidence that doing these exams routinely is helpful for women at average risk of breast cancer.)
American Cancer Society screening recommendations for women at high risk
Women who are at high risk for breast cancer based on certain factors should get a breast MRI and a mammogram every year, typically starting at age 30. This includes women who:
- Have a lifetime risk of breast cancer of about 20% to 25% or greater, according to risk assessment tools that are based mainly on family history (see below)
- Have a known BRCA1 or BRCA2 gene mutation (based on having had genetic testing)
- Have a first-degree relative (parent, brother, sister, or child) with a BRCA1 or BRCA2 gene mutation, and have not had genetic testing themselves
- Had radiation therapy to the chest when they were between the ages of 10 and 30 years
- Have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome, or have first-degree relatives with one of these syndromes
The American Cancer Society recommends against MRI screening for women whose lifetime risk of breast cancer is less than 15%.
There’s not enough evidence to make a recommendation for or against yearly MRI screening for women who have a higher lifetime risk based on certain factors, such as:
- Having a personal history of breast cancer, ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), atypical ductal hyperplasia (ADH), or atypical lobular hyperplasia (ALH)
- Having “extremely” or “heterogeneously” dense breasts as seen on a mammogram
If MRI is used, it should be in addition to, not instead of, a screening mammogram. This is because although an MRI is more likely to detect cancer than a mammogram, it may still miss some cancers that a mammogram would detect.
Most women at high risk should begin screening with MRI and mammograms when they are 30 and continue for as long as they are in good health. But a woman at high risk should make the decision to start with her health care providers, taking into account her personal circumstances and preferences.
Tools used to assess breast cancer risk
Several risk assessment tools are available to help health professionals estimate a woman’s breast cancer risk. These tools give approximate, rather than precise, estimates of breast cancer risk based on different combinations of risk factors and different data sets.
Because the different tools use different factors to estimate risk, they might give different risk estimates for the same woman. Two models could easily give different estimates for the same person.
Risk assessment tools that include family history in first-degree relatives (parents, siblings, and children) and second-degree relatives (such as aunts and cousins) on both sides of the family should be used with the ACS guidelines to decide if a woman should have MRI screening. The use of any of the risk assessment tools and its results should be discussed by a woman with her health care provider.