ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Metastatic Breast Cancer. Use the menu to see other pages. Think of that menu as a roadmap for this entire guide.
About metastatic breast cancer
Cancer begins when healthy cells change and grow out of control, forming a mass or sheet of cells called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
When breast cancer is limited to the breast and/or nearby lymph node regions, it is called early stage or locally advanced. Read about these stages in a different guide on Cancer.Net. When breast cancer spreads to an area farther from where it started to another part of the body, doctors say that the cancer has “metastasized.” They call the area of spread a “metastasis,” or use the plural “metastases” if the cancer has spread to more than 1 area. The disease is called metastatic breast cancer. Another name for metastatic breast cancer is "stage IV (4) breast cancer” if it has already spread beyond the breast and nearby lymph nodes at the time of diagnosis of the original cancer.
Doctors may also call metastatic breast cancer “advanced breast cancer.” However, this term should not be confused with “locally advanced breast cancer,” which is breast cancer that has spread to nearby tissues or lymph nodes but not to other parts of the body.
Metastatic breast cancer may spread to any part of the body. It most often spreads to the bones, liver, lungs, and brain. Even after cancer spreads, it is still named for the area where it began. This is called the “primary site” or “primary tumor.” For example, if breast cancer spreads to the lungs, doctors call it metastatic breast cancer, not lung cancer. This is because the cancer started in breast cells.
Metastatic breast cancer can develop when breast cancer cells break away from the primary tumor and enter the bloodstream or lymphatic system. These systems carry fluids around the body. The cancer cells are able to travel in the fluids far from the original tumor. The cells can then settle and grow in a different part of the body and form new tumors.
Most commonly, doctors diagnose metastatic breast cancer after a person previously received treatment for an earlier stage (non-metastatic) breast cancer. Doctors sometimes call this a “distant recurrence” or “metastatic recurrence.” This can happen at any time after someone is diagnosed with breast cancer, even a few decades later.
Sometimes, a person’s first diagnosis of breast cancer is when it has already spread to other parts of the body. Doctors call this “de novo” metastatic breast cancer or stage IV breast cancer.
Types of breast cancer
There are several types of breast cancer, and any of them can metastasize. Most breast cancers start in the ducts or lobules and are called ductal carcinomas or lobular carcinomas:
Invasive ductal carcinoma. These cancers start in the cells lining the milk ducts and make up the majority of breast cancers.
Invasive lobular carcinoma. This is cancer that starts in the lobules, which are the small, tube-like structures that contain milk glands.
Some breast cancers are made up of a combination of types of breast cancers. These are sometimes called invasive mammary cancers.
Breast cancer can develop in women and men. However, male breast cancer is rare, accounting for less than 1% of all breast cancers.
Breast cancer subtypes
Breast cancer is not a single disease, even among the same type of breast cancer. When you are diagnosed with breast cancer, your doctor will recommend lab tests on the cancerous tissue. If you have been diagnosed with metastatic breast cancer after being treated for non-metastatic breast cancer, your doctor may want to repeat the tests to see if the tumor’s cells have changed in any way. These tests will help your doctor learn more about the cancer and choose the most effective treatment plan. Metastatic breast cancer is usually not curable, but it can be treatable. Many people continue to live well for many months or years with the disease, and treatments continue to improve.
Tests can find out if your cancer is:
Hormone receptor-positive. Breast cancers expressing estrogen receptors (ER) and/or progesterone receptors (PR) are called “hormone receptor-positive.” These receptors are proteins found in cells. Tumors that have estrogen receptors are called “ER-positive.” Tumors that have progesterone receptors are called “PR-positive.” These cancers may depend on the hormones estrogen and/or progesterone to grow. Hormone receptor-positive cancers can occur at any age. However, they may be more frequent in people who have gone through menopause. Menopause is when the body's ovaries stop releasing eggs. About 60% to 75% of breast cancers have estrogen and/or progesterone receptors. If the cancer does not have ER or PR, it is called “hormone receptor-negative.”
HER2-positive. About 15% to 20% of breast cancers depend on the gene called human epidermal growth factor receptor 2 (HER2) to grow. These cancers are called “HER2-positive” and have many copies of the HER2 gene or high levels of the HER2 protein. These proteins are also called “receptors.” The HER2 gene makes the HER2 protein, which is found on the cancer cells and is important for tumor cell growth. HER2-positive breast cancers grow more quickly. They can also be either hormone receptor-positive or hormone receptor-negative (see above). Cancers that have no HER2 protein are called “HER2-negative.” Cancers that have low levels of the HER2 protein are called “HER2-low.”
Triple-negative. If the breast tumor does not express ER, PR, or HER2, the tumor is called “triple-negative.” Triple-negative breast cancers make up about 15% of invasive breast cancers. This type of breast cancer seems to be more common among younger women, particularly younger Black women. Triple-negative breast cancer may grow more quickly. Triple-negative breast cancers are the most common type of breast cancer diagnosed in people with a BRCA1 gene mutation. This means that you may be more likely to have a BRCA1 gene mutation if you have been diagnosed with triple-negative breast cancer. All people younger than 60 with triple-negative breast cancer should be tested for BRCA gene mutations. Find more information on BRCA gene mutations and breast cancer risk.
Looking for More of an Introduction?
If you would like more of an introduction, explore these related items. Please note that these links will take you to other sections on Cancer.Net:
ASCO Answers Fact Sheet: Read a 1-page fact sheet that offers an introduction to metastatic breast cancer. This free fact sheet is available as a PDF, so it is easy to print.
ASCO Answers Guide: Get this free 52-page booklet that helps you better understand breast cancer and its treatment options. The booklet is available as a PDF, so it is easy to print.
Find a Cancer Doctor. Search for a cancer specialist in your local area using this free database of doctors from the American Society of Clinical Oncology (ASCO).
Cancer Terms. Learn what medical phrases and terms used in cancer care and treatment mean.
The next section in this guide is Statistics. It helps explain the number of people who are diagnosed with metastatic breast cancer and general survival rates. Use the menu to choose a different section to read in this guide.