Types of breast cancer
Although there’s a tendency to talk about breast cancer as one disease, it is actually a group of diseases that are related because they originate in the tissues of the breast and, in some cases, move into the nearby lymph nodes and possibly other parts of the body.
It can be overwhelming at first to understand the different terms used to describe your particular type of breast cancer. But defining the type of breast cancer you have is a key first step in developing a treatment plan. This page can help you understand some of the terminology you’re likely to hear.
Breast cancers can be grouped into different types based on a number of characteristics, such as:
- Where the cancer cells first started growing in the breast, such as the lobules, which are the sacs that produce milk, or the ducts, the small tubes that carry milk from the lobules to the nipple. You may hear the term carcinoma, which describes cancer that begins in the inner lining of an organ. Most breast cancers are adenocarcinomas, a specific type of carcinoma that begins in the glandular tissue.
- Whether or not the cancer cells have moved beyond their original location. Cancers that remain inside the duct or lobule are called in situ carcinoma or carcinoma in situ. Those that have grown beyond the duct or lobule are called invasive carcinomas.
- How the cells appear under a microscope. For example, are they well-differentiated, meaning that they have relatively normal-looking cells and are not growing rapidly? Are they poorly differentiated, meaning that they lack normal features — or are they somewhere in between? This can provide clues about how aggressive the cancer is.
- The biology of the cancer, such as whether the cell surfaces have certain proteins, which can provide information about what is fueling the cancer’s growth. This information is important because it can help your care team figure out if therapies that target these proteins should be part of your treatment plan.
- For example, hormone receptors are proteins that attach to the hormone’s estrogen and progesterone. In hormone receptor-positive breast cancer, one or both of these hormones are helping cancer cells to grow.
- Tests for a protein called HER2, which promotes cell growth, can tell if the cells have increased levels of HER2.
- Cancers that test positive for hormone receptors or HER2 receptors are eligible for hormone-targeted and/or HER2-targeted treatments.
Invasive ductal carcinoma and invasive lobular carcinoma are the two main types of breast cancer. Each of these types can have characteristics mentioned in the above list. It’s also possible to have a mix of different cell features in one breast tumor.
There are many other less common types of breast cancer, too. One example is inflammatory breast cancer, an aggressive type of invasive breast cancer that usually doesn't form a lump. Symptoms can include breast swelling, thickening, or dimpling of the skin, pain, skin color changes, and heat sensations.
Breast cancer can also affect men. Male breast cancer is also rare, but an estimated 2,710 new cases were expected to be diagnosed in 2022.
How the breast cancer type is determined
Pathologists are doctors specially trained to diagnose diseases by studying their cells under a microscope. A pathologist will determine the breast cancer type using a piece of the tumor removed during biopsy, or the entire cancerous area taken out during surgery. If any nearby lymph nodes were sampled or removed, the pathologist will examine those as well. The pathologist also will perform tests that involve staining the cells, such as an immunohistochemistry test, to determine if there are hormone receptors and/or high levels of HER2.
This information will be included in your pathology report, which you and your care team will use to identify what type of breast cancer you have and come up with an appropriate treatment plan. Different test results may come back at different times. Also, if you receive a report for a sample taken during biopsy, you’ll also receive a second report once the entire breast cancer is removed during surgery.
Visit Your pathology report for detailed information about what your report will include.
In situ vs. invasive breast cancers
- In situ means that the cancer cells are contained within the breast structure where they first started growing, such as the duct.
- Invasive cancer means that the cancer cells have grown through the lining of a duct or lobule and into nearby breast tissue, the lymph nodes, and possibly to other parts of the body.
In situ breast cancer
Ductal carcinoma in situ, also called DCIS or intraductal carcinoma, is the only form of in situ breast cancer. In DCIS, cancer cells are found in the lining of the milk ducts, the tubes that carry milk to the nipple. DCIS is stage 0, meaning the cancer remains in the area where it began. The cancer will be tested for receptors to the hormones estrogen and progesterone. This can help your care team decide whether hormonal therapy would help reduce the risk of developing invasive breast cancer in the future.
Despite its name, lobular carcinoma in situ, or LCIS, isn't actually a true breast cancer. It’s a condition in which there is abnormal cell growth inside the breast’s lobules, the sacs that produce milk. LCIS raises your risk of developing breast cancer in the future (in either breast), but it’s not an immediate threat to your health. LCIS is much less common than DCIS.
Read more about DCIS and LCIS.
Invasive breast cancers
The two main types of invasive breast cancer are invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC), named for the breast structures where they originated: the ducts or the lobules. In either case, the cancer cells have grown through the wall of the duct or lobule and into surrounding tissues, lymph nodes, and possibly distant organs. IDC is much more common than ILC.
Invasive breast cancers can be classified even further depending on specific features identified by pathology testing. The types can include:
- Hormone receptor-positive breast cancer: This means that the cancer cells have receptors for either of two hormones that occur naturally in the body: estrogen, progesterone, or both. That means one or both hormones are fueling the cancer cells’ growth. Hormone receptor-positive (HR+) cancers can be treated with hormonal therapies that either lower estrogen levels or block estrogen receptors so that the cells don’t receive growth signals. Hormone receptor-negative breast cancers (HR-) do not have estrogen or progesterone receptors, so hormonal therapy won’t be helpful. HR- breast cancers tend to grow more quickly than HR+ cancers and are more common in women who haven’t yet gone through menopause.
- HER2-positive breast cancer: About 15 to 20 percent of breast cancers are HER2-positive. This means that the cancer cells have higher-than-normal levels of a protein known as HER2, also called human epidermal growth factor receptor 2. This makes cancer cells grow faster than normal. Although HER2-positive cancers tend to grow and spread more quickly than HER2-negative breast cancers, there are very effective treatments that target the HER2 protein.
- Triple-negative breast cancer: Triple-negative means that the cancer has tested negative for estrogen receptors, progesterone receptors, and HER2. So, these cancers can’t be treated with hormone therapy or HER2-targeted therapies. There are a range of chemotherapy medicines that can be used to treat this type of breast cancer. It’s not uncommon for triple-negative breast cancers to be treated with chemotherapy before surgery. There is also a targeted therapy that treats metastatic triple-negative breast cancer. About 10 to 15 percent of breast cancers are triple-negative. It’s more common in women who are under age 40, Black women, and people who have an inherited BRCA1 mutation that increases cancer risk. This type of cancer is more aggressive than hormone receptor-positive and HER2-positive breast cancers.
- Inflammatory breast cancer (IBC) is a rare type of invasive breast cancer that can be hard to detect because it usually doesn’t form a lump. Instead, it travels through the lymph system of the breast and causes visible changes to the skin, such as redness, swelling, thickening, warmth, and dimpling of the skin (like an orange peel). IBC accounts for about 1 to 5 percent of breast cancer cases, and it grows and spread quickly. It is more likely than other breast cancers to be triple-negative or HER2-positive, but it can fall into any of the above categories — so testing is important, just as it is for other types of invasive breast cancer.
You can learn more about how frequently different types of invasive breast cancer are diagnosed in the table on this page, presented by Komen.org: Prevalence and tumor characteristics of different types of invasive breast cancer.