Breast cancer can be categorized in several ways. Most often, it’s classified by where it originates and whether it moves from that spot.

According to the National Cancer Institute, about 1 in 8 U.S. women develop breast cancer at some point. It’s much less common in men, with only about 1 in 800 men likely to develop it during their lifetimes.

Your breast comprises lobules and ducts surrounded by fatty and connective tissue. The glandular lobules produce milk that’s transported to the nipple through the ducts.

Breast cancer occurs when normal cells in the lobules, ducts, or other breast tissue become damaged and grow out of control. The abnormal cells rapidly grow and accumulate, forming a tumor mass.

If a tumor grows but doesn’t spread into nearby breast tissue, it’s called a benign tumor and is not considered cancer. A malignant tumor spreads, invading surrounding tissue, and is considered cancerous.

Because it can start in lobules, ducts, or other tissue, there are many different types of breast cancer.

An easily identifiable characteristic of breast cancer is the type of cell it’s formed in:

  • Ductal carcinoma: This is formed in the cells lining the milk ducts.
  • Lobular carcinoma: This forms in the milk-producing lobules.

Another important characteristic of breast cancer is whether it invades surrounding tissue or stays where it originally formed.

Noninvasive breast lesions

Noninvasive lesions can develop in the cells of a duct or lobule but do not spread from their original location. Because of this, doctors may refer to these lesions as “in situ,” which means “in the original place.”

While cancer cells are present, many experts consider in situ disease precancerous.

There are two types of precancerous lesions: ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).

Invasive breast cancer

Invasive breast cancer develops in the cells of a duct or lobule, but it doesn’t remain where it originated. Instead, it spreads and invades surrounding tissue. Another name for it is “infiltrating.”

There are two main types of invasive breast cancer: invasive (infiltrating) ductal carcinoma (IDC) and invasive (infiltrating) lobular carcinoma (ILC).


Combining these classifications gives a descriptive name to the type of breast cancer, as outlined below:

  • Ductal carcinoma in situ: This tumor forms in ductal cells and has not spread to nearby tissue.
  • Invasive ductal carcinoma: This is a tumor that forms in ductal cells and then spreads to nearby tissue.
  • Invasive lobular carcinoma: This is a tumor that forms in lobular cells and then spreads to nearby tissue.

DCIS forms in the cells lining a milk duct. It remains there and does not spread to nearby tissues.

Doctors consider this precancer, or preinvasive, because, if left untreated, it may become invasive and spread into nearby tissue. Some cases of DCIS do not progress to invasive cancer, even without treatment. DCIS accounts for about 15–20% of all breast cancers and usually only occurs in one breast.

DCIS is often curable. It’s usually treated with a lumpectomy followed by radiation therapy or with a mastectomy.

If the cancer is hormone receptor-positive, it may be treated with tamoxifen or an aromatase inhibitor (for postmenopausal people) for 5 years after surgery. This treatment is thought to lower the risk of DCIS recurrence or invasive cancer developing in either breast.


LCIS is an uncommon formation of cells in the lobules (milk glands) in the breast. LCIS is not cancer, although it can increase your risk of developing invasive cancer.

Treatment for LCIS requires close follow-up with your doctor due to the high risk of developing invasive breast cancer.

IDC forms in the cells lining a milk duct and spreads into nearby tissue.

It’s the most common type of breast cancer, accounting for about 70–80% of all breast cancers. It’s also the most common type of breast cancer found in men.

ILC forms in the cells lining a lobule and spread into nearby tissue. It’s the second most common type of breast cancer, accounting for about 10–15% of invasive breast cancers.

ILC is more often a slow-growing tumor and may not respond to chemotherapy. However, this is not always the case.

Breast cancer is typically further classified based on the surface proteins found on the cancer cells.

When breast cancer tissue is removed from your body, it’s tested for these proteins. The cancer cells are then subtyped based on the presence or absence of surface proteins. Knowing the subtype can help your doctor determine the best treatment for your cancer.

Hormone receptor-positive

This subtype has estrogen receptors (ERs), progesterone receptors (PRs), or both. An ER-positive tumor has estrogen receptors, while a PR-positive tumor has progesterone receptors. This subtype often needs the hormones corresponding to its receptors to grow.

Learn more about hormone receptor-positive breast cancer.


This subtype has extra copies of the HER2 gene, so it produces too much of a growth hormone called human epidermal growth factor receptor 2 (HER2). This hormone allows the cancer to grow more quickly.

Learn more about HER2-positive breast cancer.


Cancers that do not have ER, PR, or HER2 receptors are called triple-negative. It’s more common in people who have a BRCA1 gene mutation, so your doctor may recommend testing for this mutation if your cancer is triple-negative.

Less common types of breast cancer are often named by the way they look under a microscope. Here’s a closer look at several less common types.

Inflammatory breast cancer (IBC)

IBC accounts for about 1–5% of all breast cancers. It’s a fast-growing, aggressive type of breast cancer that has different symptoms to most other types of breast cancer, such as breast swelling and skin thickening.

Because it doesn’t present as a lump, IBC is often mistaken for other conditions.

A blockage of the lymphatic system within the breast causes the symptoms of IBC. These symptoms tend to develop quickly, usually within 3–6 months.

Paget disease of the breast

Paget disease accounts for only up to 4% of all breast cancer cases.

Paget disease is a rare cancer that forms in the milk ducts and spreads to the skin of the nipple and areola, the skin around the nipple. This type of breast cancer is usually accompanied by DCIS or an invasive tumor within the breast.

Fibroepithelial lesions

Fibroepithelial lesions are a collection of different cell growths in the breasts. This group of lesions includes benign and cancerous growths. Due to the possibility of finding cancerous growths, doctors often recommend removing them upon discovery.

One such fibroepithelial lesion is a phyllodes tumor. This is a rare type of lesion and accounts for less than 1% of all breast tumors.

In about 75% of cases, phyllodes tumors aren’t cancerous, so they usually don’t spread beyond the breast. But they can grow quickly, and some can be considered borderline, which means they have properties that could make them cancerous at a later stage.

Tubular carcinoma of the breast

Tubular carcinoma is a subtype of invasive ductal carcinoma (IDC). This type of breast cancer gets its name due to the tube-shaped structures, which can be seen under a microscope, that make up the tumor.

The tumors are usually small (about 1 centimeter or smaller) and grow slowly.

Mucinous (colloid) carcinoma of the breast

Mucinous carcinoma, also known as colloid carcinoma, is a rare form of IDC. Close to 2% of breast cancers are “pure” mucinous carcinoma, while up to 7% of breast cancers have some component of mucinous carcinoma cells.

With this type of cancer, the tumor consists of abnormal cells that appear to float in pools of mucus.

Medullary carcinoma of the breast

Medullary carcinoma of the breast is another rare subtype of IDC. It accounts for about less than 5% of all breast cancer cases.

The tumor is typically a soft, fleshy mass rather than a lump in the breast tissue. The mass most often develops in the middle of the breast and is most often found in people with the BRCA1 mutation.

The symptoms of breast cancer can vary widely. Some types of breast cancer may not have any noticeable symptoms.

Sometimes a lump may be too small to be felt or to cause any changes to your breast or surrounding area. In these cases, cancerous cells are often first detected through screening techniques, like a mammogram.

When there are symptoms, they can include:

  • a lump or thickening of breast tissue that you can feel with your fingers
  • breast swelling or changes to your breast size or shape
  • changes to the skin on your breast, such as dimpling, redness, or skin irritation
  • the nipple turning inward or nipple pain
  • a lump in your underarm area
  • nipple discharge other than breast milk

It’s important to be familiar with how your breasts usually look and feel. This will help you notice any changes.

Follow up with a healthcare professional promptly if anything looks or feels different.

The treatment of breast cancer varies depending on many factors, such as:

  • the cancer stage
  • how far it has spread
  • tumor size
  • whether it’s hormone receptor- and HER2-positive or triple-negative
  • other underlying health conditions
  • your preferences

Possible treatment options for breast cancer include:

There are many types of breast cancer. Some types develop in the milk-producing lobules in your breast, while others grow in the cells lining the milk ducts. Some tumors are benign and noninvasive, but others can be malignant, invading nearby breast tissue.

Regular breast self-examinations and mammograms can help detect breast cancer in its early stages. Finding breast cancer that has not yet spread gives you the best chance of remaining healthy and cancer-free for many years.

According to the American Cancer Society, on average, when your breast cancer is treated before it has spread, you’re 99% as likely to be alive in 5 years as someone who does not have breast cancer.