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The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on November 04, 2020.

Breast cancer molecular types

The most common molecular subset of breast cancer is defined by its ability to respond to the female hormone, estrogen. Genomic research has led to more detailed ways to classify breast cancers, based on their genes and proteins, by dividing them into four main molecular subtypes: HER2, luminal A, luminal B and triple-negative.


One in five invasive breast cancers is HER2-positive, making this one of the more common breast cancer subtypes in the United States. HER2-positive cancers are ER- and PR-negative and human epidermal growth factor receptor 2 (HER2)-positive.

HER2-positive breast cancer cells carry too many copies of the HER2 gene, which makes HER2-protein receptors, found on breast cells. When they work normally, HER2 receptors control how a healthy breast cell grows, divides and repairs itself. When they proliferate, the receptors tell the cells to divide and grow rapidly and without control. That’s because their cells absorb too much of a substance called human epidermal growth factor 2, which energizes cell growth. Doctors often test breast cancer tissue for excess HER2-positive genes to determine whether the patient may benefit from targeted therapy options, which are designed to block HER2 from energizing cancer cell growth.

Symptoms of HER2-positive breast cancer are similar to those of other breast cancer types. They include a lump in the breast, changes to the breast’s shape, pain, swelling and abnormal discharge.

Depending on the cancer’s stage, treatment options for HER2-positive breast cancer may include a combination of surgery, radiation therapy, chemotherapy and/or administration of a targeted therapy such as the immune monoclonal antibody, trastuzumab (Herceptin®). Learn more about advanced treatments for breast cancer.

Luminal A

Luminal A is the most common subtype for every race and age. These tumors tend to be estrogen receptor (ER)-positive and progesterone receptor (PR)-positive and are typically slow growing. Treatment typically involves hormonal therapy.

Luminal B

Luminal B includes tumors that are estrogen receptor positive, progesterone receptor negative and HER2 positive. These tumors tend to grow more quickly than luminal A tumors. Luminal B breast cancers are likely to benefit from chemotherapy and may benefit from hormone therapy and treatments targeting the HER2 receptor.

Triple-negative breast cancer

What is triple-negative breast cancer? In this type of cancer, the cells do not contain receptors for estrogen, progesterone or HER2. This type of breast cancer is usually invasive and usually begins in the breast ducts.

Healthy breast cells contain receptors for the hormones estrogen and progesterone. They also contain receptors for a protein called HER2, which stimulates normal cell growth. About two out of three women with breast cancer have cells that contain receptors for estrogen and progesterone, and about 20 percent to 30 percent of breast cancers have too many HER2 receptors.

Breast cancer that is estrogen receptor (ER)- and progesterone receptor (PR)-positive can be treated with hormone therapy. Breast cancer with excess amounts of HER2 can be treated with anti-HER2 targeted therapy drugs such as trastuzumab.

In women with triple-negative breast cancer, the malignant cells do not contain receptors for estrogen, progesterone or HER2. Breast cancer that is ER-, PR- and HER2-negative cannot be treated with hormone therapy or medications that work by blocking HER2, such as trastuzumab.

Fortunately, triple-negative breast cancer can be treated with other drugs, such as chemotherapy, radiation therapy and non-HER2 targeted therapy.

Next topic: What are the stages of breast cancer?