Doctors diagnose different types of breast cancer based on many factors. Where the breast cancer started, how the cancer cells look under a microscope, and their genetic traits — such as specific mutations (changes) — are key factors in determining the type of breast cancer you have.

Knowing which type or subtype of breast cancer you have helps the oncologist (cancer specialist) predict how the cancer will grow and which breast cancer treatment options may be most effective.

Types and subtypes of breast cancer can be complex, and more than one term may apply to your diagnosis. Read on to learn more about how types of breast cancer are diagnosed.

The Anatomy of the Breast

To better understand different types of breast cancer, it’s helpful to understand the anatomy of the breast. The majority of the breast consists of glandular (milk-producing) and fatty tissues. Within the breast, there are lobes filled with lobules, or glands, where milk is made. A system of ducts connects the lobes and lobules and carries milk to the nipple. More than 80 percent of breast cancers form in the milk ducts, while other cancers form in the lobes or, less commonly, other tissues of the breast.

Understanding Breast Cancer Terminology

Most cancers are described as in situ or invasive. “In situ” is a Latin term meaning “in its original place.” In situ breast tumors are early-stage cancer and have not yet spread from the spot where the cancer began. In situ cancer may also be described as stage 0. Invasive tumors, also known as infiltrating tumors, have spread beyond the tissue where the cancer cells first began to grow. Stages 1, 2, 3, and 4 describe how invasive breast cancer is spreading. (Breast cancer stages are also sometimes rendered with Roman numerals, e.g., stage IV instead of stage 4.)

Read more about how breast cancer is staged and graded.

Doctors use many different words to describe types of cancer, usually based on the type of cell from which the tumor arose and whether it’s benign (noncancerous) or malignant (cancerous and potentially aggressive). Metastatic breast cancer or metastatic disease is when breast cancer has advanced and tumors have spread to other parts of the body — such as the liver, brain, bones, or lungs — forming secondary tumors.

According to the Breast Cancer Research Foundation, between 6 percent and 10 percent of women are initially diagnosed with stage 4 breast cancer. About 30 percent of women diagnosed with stage 0 or stage 1 breast cancer may eventually develop metastatic breast cancer, per Breastcancer.org, a nonprofit organization providing information and support to those affected by breast cancer.

Breast cancer that’s in situ hasn’t spread. If breast cancer is invasive, it has spread beyond the tissue where the tumor first started.

Most types of breast cancer are called carcinomas, which are tumors that start in epithelial cells. These cells make up the skin or line the inside of organs. Epithelial cells grow more quickly and divide more rapidly than many other types of cells, which makes them more prone to abnormal growth that leads to cancer. Because most breast carcinomas start in milk ducts or lobules, they are known as adenocarcinomas.

Molecular Subtypes of Breast Cancer: HER2, ER, and PR

Molecular subtypes of breast cancer are a relatively new type of classification that has developed out of cancer research. Doctors have long recognized that breast cancers can vary from person to person, such as how quickly they grow or how likely they are to return.

Molecular subtypes are determined by whether breast cancer cells have certain receptors. These receptors are molecules that allow hormones or proteins to bind to the outer surface of cancer cells. Understanding your molecular subtype may help guide your treatment.

Whether cancer cells have estrogen receptors (ER), progesterone receptors (PR), or human epidermal growth factor receptor 2 (HER2) proteins are key factors. These characteristics help oncologists determine how aggressive the breast cancer is and which treatments are likely to be effective. Breast cancer cells may test positive or negative for each of these molecules. In some cases, a breast cancer tumor can have features of more than one subtype.

Types of Breast Cancer

Here are some common and uncommon types and subtypes of breast cancer. Although you may not see your exact type or subtype of breast cancer listed, one or more of these characteristics likely apply to your specific case.

Your breast cancer may be described as being positive or negative for estrogen receptors, progesterone receptors, and the protein HER2.

1. Ductal Carcinoma in Situ

Ductal carcinoma in situ (DCIS) is a type of noninvasive breast cancer that began in the milk ducts and has not yet spread. DCIS is an early-stage, noninvasive cancer that’s highly treatable and accounts for 20 percent of breast cancers. There are often no symptoms with DCIS, but it can be detected on a mammogram. Left untreated, DCIS can lead to invasive cancer.

2. Invasive Ductal Carcinoma

Invasive ductal carcinoma (IDC) is the most common type of breast cancer and accounts for 80 percent of breast cancer cases. Invasive ductal carcinoma begins in the milk duct but has spread outside the duct into other tissues. Like many breast cancers, IDC may or may not have obvious symptoms, such as a lump. Without early treatment, IDC can spread to blood vessels or lymph nodes and lead to metastatic breast cancer in other parts of the body. There are many subtypes of IDC, including tubular carcinoma, medullary carcinoma, mucinous carcinoma, and papillary carcinoma.

Invasive ductal carcinoma is the most common type of breast cancer, making up about 80 percent of diagnoses.

Tubular Carcinoma

Tubular carcinoma is rare and grows slowly, which makes it very treatable. It accounts for 2 percent of all breast cancer diagnoses.

Medullary Carcinoma

This subtype causes a soft, fleshy tumor and accounts for between 3 percent and 5 percent of IDC cases. It’s more common among younger women, per Breastcancer.org, particularly those who have the BRCA1 gene. Medullary carcinoma can spread to other areas of the body.

Mucinous Carcinoma

In mucinous carcinoma (colloid), cancer cells float in a mucus-like fluid. This subtype responds well to treatment and does not usually spread aggressively. Approximately 2 percent of breast cancers are mucinous carcinoma.

Papillary Carcinoma

According to Johns Hopkins Medicine, papillary carcinoma usually develops in people over 60 years old. Under a microscope, tumors of this subtype look like finger-shaped projections. Papillary tumors can be benign, but if they are cancerous, they are generally very treatable.

3. Lobular Carcinoma In Situ

Lobular carcinoma in situ (LCIS) is a condition where abnormal cells form in the lobules of the breast. The cells in LCIS are not considered cancerous, but having LCIS indicates a higher risk of developing invasive breast cancer. LCIS doesn’t have symptoms and is usually found in a mammogram or a breast biopsy for another type of cancer.

4. Invasive Lobular Carcinoma

Invasive lobular carcinoma (ILC) accounts for about 10 percent of invasive breast cancers. ILC begins in the lobule of the breast but has spread beyond the cells of the lobe into other tissues.

5. Paget’s Disease of the Breast

This rare cancer is also known as Paget’s disease of the nipple or Paget’s disease. The condition affects the nipple and areola (the darker skin surrounding the nipple). It causes eczema-like symptoms, with scaly, itchy skin that may appear red, reddish-brown, or purple, depending on skin tone. The nipple may become flattened and have a yellow or bloody discharge. Most people who develop Paget’s disease also have cancer deeper in the breast tissues. Paget’s disease makes up 1 percent to 4 percent of breast cancer.

Read more about the potential symptoms of breast cancer.

6. Inflammatory Breast Cancer

Inflammatory breast cancer (IBC) is a rare form of breast cancer, accounting for about 1 percent to 5 percent of cases. IBC causes the breast to swell and turn red, dark purple, or reddish brown, depending on skin tone. Because of this, many people are first treated with antibiotics for suspected mastitis or an abscess and only call a specialist when the condition doesn’t improve. Symptoms become more serious quickly, sometimes within hours. IBC is a type of invasive breast cancer that grows and spreads aggressively. IBC is more common in Black women than white women, according to the American Cancer Society.

7. Phyllodes Tumors of the Breast

A rare type of breast tumor, phyllodes tumors start in the connective tissue of the breast rather than the breast ducts or lobules, like most breast cancers. Most phyllodes tumors are benign, while approximately 1 out of 4 tumors are malignant. When phyllodes tumors are cancerous, they grow quickly.

8. HER2-Positive Breast Cancer Subtype

HER2 is a gene that, when it develops a mutation, changes proteins and causes cancer cells to grow faster. Cancers that are positive for HER2 protein tend to be more aggressive, but treatments that target HER2 tend to be very effective, and most people with HER2-positive breast cancers have a good prognosis (outlook).

9. Triple-Negative Breast Cancer Subtype

About 20 percent of breast cancers are known as triple-negative breast cancer (TNBC). This subtype of breast cancer doesn’t have receptors for the hormones estrogen and progesterone or for HER2 protein. TNBC is aggressive and more common among younger women, women of African descent, and women with BRCA1 genetic mutations, per Breastcancer.org. Because it doesn’t have ER or PR receptors, hormone therapy will not work.

10. Luminal A Breast Cancer Subtype

Luminal A is the most common molecular subtype of breast cancer and occurs in 50 percent to 60 percent of breast cancers. Luminal A cancers are ER-positive, PR-positive, and HER2-negative. Luminal A cancers usually grow slowly and respond well to breast cancer treatment, including medications that target hormones.

11. Luminal B Breast Cancer Subtype

Luminal B cancers are ER-positive or PR-positive and can be either HER2-positive or HER2-negative. The luminal B subtype occurs in 15 percent to 20 percent of breast cancers and is aggressive. They have high levels of the protein Ki-67, which helps cancer cells grow faster. HER2 targeted therapy, along with other cancer therapies is used to treat luminal B breast cancers.

Find Your Team

On MyBCTeam, the social network for people with breast cancer and their loved ones, more than 73,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

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