There are many ways in which doctors can categorize and describe breast cancer. Finding out your breast cancer type helps you and your cancer care team understand which treatments may work best and what your prognosis (outlook) is likely to be.
There are many different types and subtypes of breast cancer. The type you have depends on where the tumor occurred and how the cancer cells look.
Breast cancer can also be categorized based on whether or not the cells contain certain genes or proteins.
Different types of cancer may lead to different sets of symptoms.
Breast cancer treatments may be more or less likely to work based on the type of cancer you have.
Types of breast cancer
There are more than 30 different subtypes of breast cancer. However, most tumors fall into a few broad categories. Breast cancer can be:
- Ductal (developed from cells that form the milk ducts) or lobular (started in the breast lobules that make milk).
- Invasive (spreading into the surrounding tissue) or in situ (cells have not yet started to spread).
Ductal carcinoma in situ or DCIS is considered early or “stage 0” breast cancer. It makes up about 15 to 20% of breast cancer diagnoses. If DCIS is left untreated, it can become more aggressive and transform into invasive ductal carcinoma (IDC).
Invasive ductal carcinoma or IDC is the most common breast cancer type, making up three out of four cases of breast cancer. It often leads to a solid lump in the breast. While IDC first develops in the milk ducts, it eventually spreads outside the duct into the breast tissue. It may also metastasize (spread to other parts of the body).
There are several subtypes of IDC, including:
- Medullary carcinoma — About one out of 20 women with breast cancer have medullary carcinoma, which often leads to a good prognosis.
- Mucinous carcinoma — This subtype, which makes up less than 2% of all breast tumors, includes cancer cells that produce a lot of mucus. This type of cancer is less likely to spread and is often easily treated.
- Tubular carcinoma — Tubular carcinomas are rare, making up about 2% of breast cancer cases. They don’t often grow very quickly or aggressively.
- Metaplastic carcinoma — This rare form of cancer develops when one type of breast cancer such as IDC changes into another type of breast cancer such as sarcoma.
Invasive lobular carcinoma
In cases where breast cancer appears in both breasts, it is most likely to be invasive lobular carcinoma or ILC. About 10 to 15% of invasive breast cancers are ILC.
There are also several ILC subtypes, diagnosed based on what the cells look like and how they grow. Subtypes include classic, solid, alveolar, tubulolobular, and pleomorphic ILC. This cancer can be hard to diagnose early and may have already begun to spread by the time it is detected.
Inflammatory breast cancer
This type of cancer is much less common. Only about 1 to 5% of breast cancers fall into this category.
Inflammatory breast cancer leads to different symptoms than other breast cancer types — while most breast cancers cause a lump or nipple discharge, inflammatory breast cancer often leads to redness, bruising, or swelling in the breast. The skin may also become dimpled or pitted.
Inflammatory breast cancer usually grows and spreads quickly.
Paget disease of the breast
This cancer develops from cells in the skin of the nipple or areola (darker skin that surrounds the nipple). It can lead to itching, flaking, thickened skin, or redness. Some people also experience nipple discharge.
Paget disease usually occurs alongside other tumors within the breast, such as DCIS, IDC, or ILC. About 1 to 4% of these other cancers are accompanied by Paget disease of the breast.
This type of breast cancer is very rare. Only one out of 100 women with breast cancer has breast sarcoma. This cancer often leads to poor outcomes, but treatment with a lumpectomy (surgical removal of the tumor and a small amount of normal breast tissue) and radiation therapy may lead to a better outlook.
Phyllodes tumors are extremely rare. They develop in the breast’s connective tissue (the tissue that connects and maintains the shape of other cells and tissues). Phyllodes tumors can be either malignant (cancerous) or benign (non-cancerous).
HER2 and hormone receptor status
When a breast tumor is diagnosed, doctors will test to see whether the cancer cells contain certain genes or proteins. This information can also help guide treatment decisions.
There are three main proteins that doctors look for: HER2, estrogen receptor (ER), and progesterone receptor (PR). Breast cancer is grouped into categories based on whether the cells have these proteins:
- HER2-positive breast cancer — When breast cancer cells have high levels of HER2, they rely on this protein to grow. HER2-positive tumors tend to grow more quickly and aggressively. However, this cancer can be treated with targeted therapy drugs that block HER2 and prevent the cancer cells from dividing.
- Hormone receptor-positive breast cancer — These cancers contain high levels of ER, PR, or both. This type of breast cancer uses the hormones estrogen and/or progesterone to grow. It is often treated with hormone therapy, which can prevent hormones from interacting with cancer cells, starving the tumor.
- Triple-negative breast cancer — This type of breast cancer does not contain HER2, ER, or PR. Triple-negative breast cancer or TNBC is harder to treat because most targeted therapies and hormone therapy won’t be effective. Most people with this cancer receive chemotherapy or take part in clinical trials.
Doctors also commonly run tests to look for mutations in genes like BRCA1, BRCA2, or TP53. This information tells you if your breast cancer was caused by genetic factors that are passed down within families and whether your family members have an increased risk of cancer. Additionally, certain breast cancer treatments may work better to treat tumors with specific mutations. For example, drugs called PARP inhibitors can more effectively treat cancer cells that contain BRCA mutations.
If you have been diagnosed with breast cancer, talk to your doctor about which type you have. Your oncologist can help you understand how this affects your treatment plan and what it might mean for your prognosis.