Epidemiology is the study of how often a health condition affects various groups of people and why. Understanding the epidemiology of breast cancer helps scientists and doctors create new and better ways to prevent and treat it.
Even if you’re not a scientist, knowing a bit about breast cancer epidemiology can help you understand your own risks. And you’ll be better prepared if you or a loved one is diagnosed with breast cancer.
How Do Doctors Characterize Breast Cancers?
Doctors divide breast cancers into types based on where in the breast the cancer starts, the types of hormone receptors on the cancer cells, and how the cancer spreads. These things help determine what treatments doctors can use, as well as your outlook for recovery.
Breast cancers can be noninvasive or invasive. Breast cancer is noninvasive when it hasn’t spread beyond the area in the breast where it began.
Ductal carcinoma in situ (DCIS) is an early type of breast cancer that hasn’t spread beyond the lining of the milk ducts. One in 5 breast cancers is DCIS.
Invasive cancers start in the milk ducts or in the breast lobules (the glands that make milk) but have spread to other parts of the breast or to the lymph nodes in your armpit. Up to 80% of all breast cancers are invasive cancers of the milk duct (called invasive ductal carcinomas). Cancers that start in the lobules are called invasive lobular carcinomas.
Doctors further characterize breast cancers by what type of receptors their cells contain. Receptors are proteins that bind to certain substances in your blood that can affect cell growth.
Estrogen- or progesterone-receptor-positive breast cancers grow when they’re exposed to the hormones estrogen or progesterone. Around 2 of every 3 breast cancers are this type.
HER2-positive breast cancer is a type of cancer in which your body makes too much of a protein called HER2. This can drive breast cancer cells to grow quickly. About 20% of breast cancers are HER2-positive.
Triple-negative breast cancer isn’t affected by estrogen or progesterone and doesn’t involve extra HER2. This cancer grows faster and is harder to treat than other types. About 15% of all breast cancers are triple-negative.
Inflammatory breast canceris a rare kind of breast cancer that spreads fast. The cancer cells block lymph vessels, which makes your breast swell and turn red. Only 1% to 5% of breast cancers are this type.
There are other rare forms of breast cancer:
- Paget disease of the nipple starts in milk ducts and spreads to the nipple. About 1% to 3% of breast cancers are this type.
- Angiosarcoma starts in cells lining blood vessels or lymph vessels. Less than 1% of breast cancers are this type.
- Phyllodes tumors grow in the connective tissue of the breast. They make up less than 1% of breast cancers.
Metastatic breast cancer happens when breast cancer cells escape from the breast area and form tumors in other parts of the body. Most often, this happens in the bones, brain, lungs, or liver. About 30% of women who are diagnosed with a less-advanced breast cancer eventually get metastatic breast cancer.
What Are the Risk Factors for Breast Cancer?
Things like your age and family history can raise your risk for breast cancer. Some of the risk factors you can control. Others, you can’t.
Just because you have these risks doesn’t mean that you’ll get breast cancer. It's also possible to have no risks and still get breast cancer.
Most breast cancers are diagnosed in women older than 50. Other risks include:
- A personal or family history of breast cancer
- Starting your period before age 12 or starting menopause after 55
- Previous radiation therapy to your chest or breasts
- Being pregnant for the first time after age 30 or not breastfeeding
- Taking birth control pills or hormone therapy
- Drinking too much alcohol
- Being overweight or obese
Who Gets Breast Cancer?
Breast cancer is most common in middle-aged and older women. Every woman has a 1 in 8 chance of being diagnosed with this cancer at some point in her lifetime.
The odds that a person will be diagnosed with breast cancer in the next 10 years increase with age:
- Age 30: 1 in 204 chance
- Age 40: 1 in 65 chance
- Age 50: 1 in 42 chance
- Age 60: 1 in 28 chance
- Age 70: 1 in 24 chance
These numbers are based on large groups of women. Your own chance of getting breast cancer might be lower or higher, depending on your specific risks.
Men get breast cancer too, though much less often than women. A man’s chance of being diagnosed in his lifetime is about 1 in 833.
White women are more likely to get breast cancer than women of other races. But Black women are more likely to have types that grow faster. They also get breast cancer at an earlier age and die from it more often than white women. American Indian/Alaska Native, Asian, and Hispanic women have a lower risk of breast cancer than women of other races.
How Is Breast Cancer Detected?
Mammograms are the best tool to detect breast cancer early, when it’s easiest to treat. This screening test uses X-rays to find cancer in people who don’t have symptoms. When a mammogram shows a spot that may be cancer, your doctor will use other tests to confirm whether it’s cancer and to see if the cancer has spread. These tests include magnetic resonance imaging (MRI), ultrasound, and biopsy.
Different organizations have their own guidelines for when women should start to have mammograms and how often they should get these tests. The U.S. Preventive Services Task Force recommends them once every 2 years from ages 50-74 for women who are at average risk for breast cancer.
The American Cancer Society recommends yearly mammograms for women ages 45-54. Once you turn 55, it suggests mammograms every other year for as long as your health is good and you’re expected to live at least 10 years.
What Are the Survival Rates for Breast Cancer?
Early detection and new treatments mean more people survive breast cancer than in the past. The relative survival rate for all breast cancers is more than 90 percent. “Relative survival” means that people with breast cancer are 90 percent as likely to live for 5 years as people without this cancer.
Cancers that haven’t spread beyond the breast have a better outlook. The 5-year relative survival rate for these early breast cancers is 99 percent.
Once breast cancer has spread to the lymph nodes or areas near the breast, the 5-year relative survival rate is 86 percent. The 5-year survival rate for metastatic cancer is 29 percent, though some people live for many years with this type of cancer.
Remember that these numbers are based on large groups of people. Your outlook is based on your cancer type and treatment.
How Does Race Affect Breast Cancer Survival Rates?
Breast cancer deaths have dropped more than 40 percent over the last 30 years because doctors are finding them earlier and have better treatments. But not everyone has had equal benefits from these gains.
Black women often get breast cancer at a younger age than white women. They’re also more likely to have fast-growing breast cancers like triple-negative breast cancer. And they’re 41 percent more likely to die from breast cancer than white women.
Genetic differences, plus a lack of access to health insurance and health care, are among the reasons for these differences.
How Is Breast Cancer Treated?
Breast cancer treatment varies based on your cancer type, tumor size, and other factors, such as whether hormones play a role in its growth. Older treatments like surgery, radiation, and chemotherapy aim to kill as many cancer cells as possible. Most people still get one or more of these treatments.
Newer therapies are more targeted to unique differences that happen in some types of breast cancer.
Your doctor can treat breast cancers affected by hormones with medicines like tamoxifen and aromatase inhibitors. These drugs lower estrogen levels to prevent this hormone from fueling the cancer’s growth.
If you have HER2-positive breast cancer, your doctor may use the drugs pertuzumab (Perjeta) or trastuzumab (Herceptin). They attach to the HER2 protein on your breast cancer cells to stop their growth. Other targeted medicines block proteins like CDK4 and CDK6, mTOR, and PI3K that help breast cancer cells grow and divide.
Pembrolizumab (Keytruda) blocks a protein called PD-1 that stops your immune system from attacking cells in your body. Blocking this protein takes the brakes off your immune system so it’s easier for it to attack cancer cells.
Other treatments target gene changes in your cancer cells. Olaparib (Lynparza) and talazoparib (Talzenna) are treatments for breast cancers that test positive for the BRCA1 and BRCA2 genes.
Genetic tests and other kinds of tests can show your doctor whether these targeted treatments may help you.
Factors That Affect Treatment and Outcomes
It can be hard to predict how well you’ll do after a breast cancer diagnosis. A few things might affect this, including:
- Your age
- Your health
- How fast-growing your cancer is and where it has spread
- What kind of treatments you get
- How well you respond to those treatments
- Whether your cancer cells have hormone receptors or too much HER2
Breast cancer affects not only your health, but also your quality of life. You might have physical symptoms from the cancer or its treatments, as well as emotional symptoms like fear and anxiety.
These five tips can help you feel better during and after cancer treatment:
- Ask for help when you need it.
- Relax with deep breathing, yoga, or meditation.
- Exercise as much as you can.
- Eat a healthy diet.
- Join a support group.
