What are the Molecular Subtypes of Breast Cancer?

Medically Reviewed By: Adrienne G. Waks, MD

Treatment for breast cancer is generally based on the type of breast cancer, its stage, and other factors. Increasingly, care teams are devising treatment plans by looking at the molecular subtype of each breast cancer.

The various subtypes of breast cancer behave and grow in different ways, and can be divided based on different genes they express. The four main molecular subtypes are:

  • Luminal A breast cancer
  • Luminal B breast cancer
  • Triple-negative/basal-like breast cancer
  • HER2-positive breast cancer

Luminal A

Luminal A breast cancer is the most common molecular type of breast cancer. This type of cancer tends to grow slowly and has a good prognosis.

Luminal A tumors often:

  • Are hormone-receptor positive (estrogen-receptor and/or progesterone-receptor positive)
  • Are HER2 negative, meaning they do not test positive for higher-than-normal levels of HER2 receptors on the surface of the cancer cell
  • Have low levels of the protein Ki-67, which helps control the growth and formation of cancer cells

Drugs that lower or block estrogen in the body tend to be useful in treating this type of cancer.

Luminal B

Luminal B tumor cells grow faster and are considered more aggressive.

Luminal B tumor cells are hormone-receptor positive (including estrogen-receptor and/or progesterone-receptor positive), and either HER2-positive or HER2-negative, with high levels of the protein Ki-67.

In addition to drugs that lower or block estrogen, this type of tumor is often treated with chemotherapy that stops the reproduction of cancer cells and other therapies that target the HER2 protein.


As its name suggests, this type of tumor has cells that look similar to those of the outer (basal) cells surrounding the mammary ducts.

These tumor cells are hormone-receptor negative (estrogen-receptor and progesterone-receptor negative) and HER2-negative.

This type of cancer is more likely to occur in younger, Black, non-Hispanic Black, and African American women, and is more common among women with BRCA1 gene mutations.

Researchers are working to develop therapies to treat triple-negative breast cancer more effectively. Treatment typically includes a combination of surgery, radiation therapy, and chemotherapy.


HER2-positive breast cancers tend to grow faster than luminal breast cancers.

These tumors are typically hormone-receptor negative (estrogen-receptor and progesterone-receptor negative) and HER2-positive.

HER2-positive breast cancer is often successfully treated with targeted therapies aimed at the HER2 protein such as trastuzumab (Herceptin), a specially made antibody that works against HER2-positive cancer cells by attaching to the HER2 protein on the surface of the cancer cells to slow or stop their growth.

The Susan F. Smith Center for Women’s Cancers at Dana-Farber creates powerful possibilities for patients by bridging compassionate care and world-class research. Learn more here about breast cancer treatment.

About the Medical Reviewer

Adrienne G. Waks, MD

Dr. Waks received her undergraduate degree from Princeton University in 2006 and her MD degree from Harvard Medical School in 2011. She completed residency training in internal medicine at Brigham and Women's Hospital, where she subsequently served an additional year as a Chief Resident in Internal Medicine. She completed fellowship training in medical oncology at Dana-Farber/Partners CancerCare, then joined the staff of the Breast Oncology Center at Dana-Farber Cancer Institute.

1 thought on “What are the Molecular Subtypes of Breast Cancer?”

  1. Always interested in seeing the latest research on Breast Cancer. My mom went yearly for her mammo and one year they found the cancer and by the end of the week it was determined to be HER2+ S4. She came to DF in the final two years of her life for experimental treatment. We will always be thankful for the care she received.

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