According to the Centers for Disease Control and Prevention (CDC), breast cancer is the leading cause of cancer among women in the U.S. In 2019, roughly 271,270 new cases of breast cancer will be diagnosed in the U.S. About 1 in 8 women will develop invasive breast cancer over a lifetime, on average. However, today, 9 out of 10 women with breast cancer are still alive five years after their diagnosis due to earlier detection and advanced therapies.
What is Breast Cancer?
Cancer is a group of many related diseases that begin in cells, the body's basic unit of life. The body is made up of many types of cells, and normally, cells grow and divide to produce more cells only when the body needs them. Sometimes, however, cells keep dividing when new cells are not needed. These extra cells form a mass of tissue, called a growth or tumor. There are two types of tumor: benign and malignant.
- Benign tumors are not cancer. They can usually be removed, and, in most cases, they do not come back. Cells from benign tumors do not spread to other parts of the body, and are not a threat to life.
- Malignant tumors are cancer. Cells in these tumors are abnormal; they divide without control or order, and can invade and damage nearby tissues and organs. Cancer cells can break away from a malignant tumor and spread by entering the bloodstream or the lymphatic system. The spread of breast cancer is called "metastatic breast cancer".
When cancer arises in breast tissue and spreads outside the breast, cancer cells are often found in the lymph nodes under the arm. If the cancer has reached these nodes, it means that cancer cells may have spread to other parts of the body, including other lymph nodes and other organs, such as the bones, liver, or lungs.
When cancer spreads from its original location to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if breast cancer spreads to the brain, the cancer cells in the brain are actually breast cancer cells. The disease is called metastatic breast cancer.
What Causes Breast Cancer?
The exact causes of breast cancer are not known. However, studies show that the risk of breast cancer increases with age, and that, along with being a woman, is the greatest risk factor. The disease is very uncommon in women under the age of 35. Most breast cancers occur in women over the age of 50, and the risk is especially high for women over age 60. Breast cancer occurs more often in white and black women compared to Hispanic, Asian/Pacific Islander, or American Indian/Alaska Native women (Table 1).
Table 1. Female Breast Cancer Rate per 100,000 women
Age-Adjusted Rate (per 100,000 women)
American Indian/Alaska Native
Source: CDC. United States Cancer Statistics: Data Visualizations https://gis.cdc.gov/Cancer/USCS/DataViz.html
Women with the following conditions also have an increased risk for breast cancer:
- Personal history of breast cancer - Women who have had breast cancer face an increased risk of getting breast cancer in the other breast.
- Family history, genetic mutations - Risk for developing breast cancer increases if a close relative (mother, sister, or daughter) has had breast cancer, especially at a young age. Risk is also elevated in women with multiple family members on either her mother’s or father’s side, or if she has a first-degree male relative with breast cancer.
- Genetic mutations - Genetic testing can sometimes show the presence of specific genetic changes (BRCA1, BRCA2) that increase the risk of breast cancer and possibly ovarian cancer. Doctors may suggest ways to try to delay or prevent breast cancer, or to improve the detection of this disease in women who have these changes in their genes.
- Certain breast changes - Having a diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase the risk of breast cancer. In situ means the cancer has not spread.
Other factors associated with an increased risk for breast cancer include:
- Estrogen - Evidence suggests that the longer a woman is exposed to estrogen (made by the body, taken as a drug, or delivered by a patch), the higher the risk of developing breast cancer. The risk is somewhat increased among women who began menstruation early (before age 12), experienced late menopause (after age 55), never had children, or took Hormone Replacement Therapy (HRT) for a long time.
- Late childbearing - Women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.
- Breast density - Breast cancers nearly always develop in lobular or ductal (dense) tissue rather than in fatty tissue. Breast cancer is more likely to occur in breasts that have a lot of dense tissue. It is also more difficult to see abnormal areas on a mammogram when breasts are dense. Women may elect to use have 3D mammogram if they have dense breast tissue. The 3D mammogram makes it easier to see breast cancers because the image is clearer for doctors to see.
- Radiation therapy - Women whose breasts were exposed to radiation during radiation therapy before age 30 (for example, treatment of Hodgkin’s lymphoma) are at an increased risk for developing breast cancer. Studies show that the younger a woman was when she received treatment, the higher the risk for developing breast cancer later in life.
- Diethylstilbestrol (DES) use - Between 1940 to 1971, DES was given to some pregnant women in the U.S. to prevent miscarriage. These women, as well as their daughters are at an increased risk.
- Alcohol use - Studies show that a woman’s risk for breast cancer increases with the more alcohol she drinks. In women who drink more than 2 drinks per day, they have a 50% higher risk of developing breast cancer than women who do not drink.
Many risk factors for developing breast cancer cannot be changed, but some can. Being overweight, excessive alcohol use, taking certain hormones, having a first pregnancy after age 30, never having a baby or never breastfeeding, and smoking are risk factors that may elevate the risk for breast cancer.
It is important to know that many of the women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older. And most women, about 88%, are never diagnosed with breast cancer.
Screening for Breast Cancer
Breast cancer screening has been shown to decrease the risk of dying from breast cancer, and deaths from breast cancer have decreased over the past few decades. Women can take an active part in the early detection of breast cancer by having regularly scheduled screening mammograms.
Clinical breast exams (performed by health care professionals) and monthly breast self-exams are no longer recommended by expert groups. However, some groups do encourage breast "self awareness", which includes breast cancer education, knowing what is normal for your breasts, and what to do if you notice a change.
A screening mammogram, an X-ray of the breast, is the best tool available for finding breast cancer early, before symptoms appear. Mammograms can often detect a breast lump before it can be felt. If an area of the breast looks suspicious on the screening mammogram, additional diagnostic mammograms or a magnetic resonance image (MRI) may be needed. Depending on the results, the doctor may advise the woman to have a breast biopsy.
Recommendations for when to start mammograms and how often to have them vary among leading healthcare organizations. In women aged 50 to 74 with an average risk of breast cancer, most recommendations suggest a screening mammogram every year or every 2 years. These screenings may occur more frequently in higher risk women, or using an MRI instead of a mammogram.
Starting at age 40, discuss breast cancer screening with your doctor to determine the best frequency based on your age, family history, and other risk factors. Most guidelines recommend to continue screening mammograms in women with a life expectancy of at least 10 more years.
Symptoms of Breast Cancer
Early breast cancer usually does not cause pain, and when breast cancer first develops, there may be no symptoms at all. As the cancer grows, it can cause changes in the breast.
Breast cancer signs or symptoms may include:
- A lump or thickening in or near the breast or in the underarm area
- A change in the size or shape of the breast
- Nipple discharge or tenderness, or the nipple pulled back (inverted) into the breast
- Ridges or pitting of the breast (the skin looks like the skin of an orange)
- A change in the way the skin of the breast, areola, or nipple looks or feels (for example, warm, swollen, red, or scaly).
- Pain in any area of the breast
Any symptoms such as those listed should be reported to a doctor. Most often, they are not cancer, but it's important to check with the doctor so that any problems can be diagnosed and treated as early as possible.
Related: Breast Changes and Conditions
Diagnosis of Breast Cancer
A doctor may perform one or more breast examinations:
- Clinical breast exam - Involves the doctor carefully feeling the lump and the tissue around it. Benign lumps often feel different from cancerous ones. The doctor can examine the size and texture of the lump and determine whether the lump moves easily. Clinical breast exams are no longer recommended as part of a routine screening by some experts groups because mammography gives a more accurate result.
- Mammography - X-rays of the breast that can give the doctor important information about a breast lump.
- Ultrasonography (ultrasound) - Can often show whether a lump is a fluid-filled cyst (not cancer) or a solid mass (which may or may not be cancer). This exam may be used along with mammography.
- Biopsy - Involves the removal of fluid or tissue from the breast so the doctor can make a diagnosis.
- Fine-needle aspiration - A thin needle is used to remove fluid and cells from a breast lump. If the fluid is clear, it may not need to be checked by a lab.
- Needle biopsy - A needle is used to remove tissue from an area that looks suspicious on a mammogram. The tissue is sent to a lab to be checked by a pathologist for cancer cells.
- Surgical breast biopsy - Incisional biopsy involves cutting out a sample of a lump or suspicious area using anesthesia to keep the procedure pain-free. Excisional biopsy involves removing all of the lump or suspicious area and an area of healthy tissue around the edges. A pathologist then examines the tissue under a microscope to check for cancer cells.
When Cancer Is Found
Breasts are made up of lobules that make breast milk and the ducts that carry the milk to the nipples.
The earliest form of breast cancer is called ductal carcinoma in situ (DCIS), which is breast cancer that has not grow outside of the lining of the breast milk ducts. DCIS cancers still need to be treated as they may grow into surrounding tissue if not treated. The pathologist is able to tell if the cancer is ductal or lobular, and whether it has invaded nearby tissues in the breast (called invasive breast cancer). DCIS should also be checked for hormone receptors.
Other types of rare breast cancer include Paget’s disease of the breast and inflammatory breast cancer.
Lobular carcinoma in situ (LCIS) is a risk factor for developing cancer but is not considered a cancer itself.
Most breast cancers are invasive when they are found and they have grown outside the ducts or lobules into the surrounding tissue. Locally invasive breast cancer has only spread within the breast tissue, while metastatic cancer has traveled through the blood or lymph to other areas such as the lungs, bone, or liver.
Certain proteins are tested for by a pathologist once breast cancer is detected. It is important to test for these receptors on the cells so that the most appropriate cancer treatment can be received.
- Hormone receptor tests of the tissue look for estrogen (ER+) and progesterone receptors (PR+).
- This helps to determine the potential response of the cancer to hormonal therapy that blocks the actions of estrogen.
- Breast cancers can be positive for one, both, or none of these receptors.
- About 2 out of every 3 breast cancers are hormone receptor-positive (HR+). Hormone-negative cancers often grow faster than hormone-positive cancers.
- HER2 receptors (the human epidermal growth factor receptor 2 or HER2 gene) is a specialized protein found on breast cancer cells that controls cancer growth.
- HER2-positive breast cancer has an excess of HER2 genes or receptors.
- It is present in about 1 out of every 5 invasive breast cancers.
- The test for this gene determines the risk of the breast cancer returning and can help to determine the best treatment that is directed against HER2.
Other tests (lab tests and x-rays) are sometimes performed to predict the progression of the cancer. Examinations of the bones, liver or lungs may be performed because the breast cancer may spread to these areas.