The type of breast cancer you have determines which treatment you get. People with the same type of breast cancer are usually treated in a similar way.
Types Based on Where Cancer Starts or Spreads
One of the ways doctors describe breast cancer is based on where in your body it starts or spreads.
Breast cancers are often a type of carcinoma called an adenocarcinoma. These cancers start in the cells lining the milk ducts (ductal carcinoma) or the glands (called lobes) that produce milk (lobular carcinoma).
Ductal Carcinoma. Ductal carcinoma is cancer of the cells that line the milk ducts in your breast.
Ductal carcinoma in situ (DCIS) is the earliest form of ductal carcinoma. "In situ" means it's only in the milk ducts, and isn't likely to spread to other parts of your body. About 1 in 5 people who are newly diagnosed with breast cancer have DCIS. This type is very curable.
Invasive ductal carcinoma (IDC) is the most common type of breast cancer, affecting about 80% of people who are diagnosed. "Invasive" means the cancer is able to spread outside of the milk duct where it started.
There are several subtypes of invasive ductal carcinoma:
- Medullary carcinoma. This rare type of invasive breast cancer is named "medullary" because it looks like the soft grayish tissue in your brain, called the medulla. Less than 5% of breast cancers are this type.
- Mucinous carcinoma. Mucin is an ingredient in mucus, the slimy substance that keeps your organs and tissues from drying out. In this type of breast cancer, you have lots of mucin around the cancer cells. Less than 2% of all breast cancers are true mucinous carcinomas. Another name for this cancer is colloid carcinoma.
- Tubular carcinoma. About 1% to 2% of invasive breast cancers are this type, which gets its name from tube-like structures inside the cancer cells. Tubular carcinomas often grow slowly and are very treatable.
- Papillary carcinoma. The name "papillary" comes from the finger-like growths, called papules, that stick out from these cancer cells. Only about 1% of breast cancers are papillary carcinomas. This type is more likely to affect older women.
- Cribriform carcinoma. This rare breast cancer type has a unique pattern of holes between the cancer cells. About 5% to 6% of invasive breast cancers contain cribriform carcinoma.
- Lobular carcinoma. In lobular carcinoma, abnormal cells grow in the lining of your breast's milk-producing glands (lobules). Invasive lobular carcinoma (ILC) is the second most common form of breast cancer diagnosed in the U.S. About 10% of invasive breast cancers are this type. ILC starts in the lobules and spreads to tissue around them. It can get into your lymph nodes and spread to other parts of your body. Another name for ILC is infiltrating lobular carcinoma.
You might also hear about lobular carcinoma in situ (LCIS). But LCIS isn't really cancer, and won't spread outside of the lobule. Doctors usually find it when they do a breast biopsy.
Inflammatory Breast Cancer. This rare type makes up less than 5% of all breast cancers. Its symptoms are different from those of other breast cancers. Cancer cells block lymphatic vessels in your breast (similar to blood vessels, except they carry lymphatic fluid). This causes the skin to swell, turn red, and thicken. Parts of your breast might look like the skin of an orange. Inflammatory breast cancer can spread quickly.
Phyllodes Tumor of the Breast. These rare tumors grow in the breast's connective tissue. They're more common in women who have an inherited condition called Li-Fraumeni syndrome. Only 1 in 4 phyllodes tumors are cancer. The rest are noncancerous (benign).
Paget's Disease. This rare type accounts for less than 5% of all breast cancers in the U.S. It grows in the nipple and the area around it (areola). The skin of your nipple and areola may get scaly, red, and itchy. Most women with Paget's disease also have ductal or invasive breast cancer.
Metastatic Breast Cancer. Metastatic means the cancer has spread beyond your breast. Doctors also call this "advanced" or "stage 4" cancer. The most common places for breast cancer to spread are to the liver, brain, bones, or lungs.
Types Based on the Cancer's Genes or Hormones
When you're diagnosed with breast cancer, your doctor will test your cancer cells to see whether they grow in response to hormones like estrogen or progesterone, or if they contain certain genes. These tests help your doctor find the treatment that works best against your cancer.
HER2-positive. About 1 out of every 5 breast cancers tests positive for human epidermal growth factor receptor 2 (HER2). This protein helps cancer cells grow. HER2-positive breast cancers are often more aggressive than other types. A group of drugs that include pertuzumab (Perjeta) and trastuzumab are effective against these cancers.
Hormone receptor-positive or negative. Some breast cancer cells have areas on their surface (receptors) that attach to the hormones estrogen (ER) or progesterone (PR). These hormones help the breast cancer cells grow:
- ER-positive breast cancers have estrogen receptors.
- PR-positive breast cancers have progesterone receptors.
- Hormone receptor-positive means the cancer has one or both of these hormone receptors.
- Hormone-receptor negative means the cancer doesn't have ER or PR receptors.
Triple negative. Around 15% of breast cancers are this type. Triple-negative breast cancer doesn't have receptors for estrogen, progesterone, or HER2. This makes it harder to treat.
Once you learn your breast cancer type, ask your doctor what it means for your outlook and what medicines are available to treat it.