Luminal B Breast Cancer

April 10, 2025

This page was reviewed under our medical and editorial policy by Nikhila Kethireddy, M.D., assistant clinical professor, and Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Breast cancer is grouped into certain subtypes based on similarities in genes, proteins and other molecules found in the cancer cells. Luminal B breast cancer is one of these molecular subtypes. It accounts for about 10% of breast cancer cases.

Molecular subtypes of breast cancer also include luminal A, triple-negative and HER2-enriched breast cancer.

Knowing the patient’s breast cancer subtype helps the care team plan treatments, track how well the treatments are working and understand the person’s prognosis, or likelihood of recovery.

What Is Luminal B Breast Cancer?

Doctors look for three main molecular elements when categorizing breast cancer as luminal B.

Estrogen receptor-positive (ER-positive): Cells have different proteins that hormones in the body attach to, and these are called hormone receptors. Estrogen receptors (ERs) are a type of hormone receptor present on some of the luminal B cancer cells. Estrogen binds to ERs, which helps promote cancer cell growth.

Progesterone receptor-negative (PR-negative): Luminal B breast cancer cells typically do not have progesterone receptors (PRs) that progesterone can bind to.

Either HER2-positive (HER2+) or high Ki-67 levels: Luminal B used to be considered HER2+, but doctors now categorize the disease as having either high levels of the HER2 protein (meaning it is HER2+) and/or high levels of the Ki-67 protein. It may also have both. These proteins, in high amounts, help the cancer cells rapidly reproduce.

If breast cancer cells have either estrogen or progesterone receptors, the cancer is known as hormone receptor-positive (HR+) breast cancer. Since luminal B has estrogen receptors and can also have HER2+ (or be high in Ki-67), it is sometimes referred to as HR+/HER2+ breast cancer.

An expert called a pathologist tests a small sample of the patient’s breast tissue removed during a breast biopsy procedure to find out if the cancer is luminal B. The results are shared with the patient and doctor. The pathologist may also perform gene expression testing to discover if genes or gene mutations (changes) are present that help the cancer cells grow and thrive.

Luminal B Breast Cancer Symptoms

Not all people experience symptoms of breast cancer, especially when it is in the early stages. Screening mammograms are used to look for changes in breast tissue that may be indicators of the disease.

If luminal B symptoms do occur, they may include:

• A breast lump or armpit mass that is either hard with uneven edges or soft and round
• Thick, flaky, dry breast or nipple skin that may be red in color
• An inflamed (swollen) breast
• Changes in breast shape or size
• Nipple pain or a pulling sensation
• Nipple discharge that is not breast milk
• An inward-turned nipple
• Breast pain

Telling the doctor about these or other breast symptoms as soon as possible is highly recommended because breast cancer found in the early stages is often easier to treat than more advanced cases of the disease. The doctor is able to schedule diagnostic tests to find out the underlying cause of the symptoms.

Luminal B Breast Cancer Treatment

Like the majority of breast cancers, luminal B is commonly treated with breast-conserving surgery (lumpectomy) that removes part of the breast and sometimes axillary lymph nodes (in the armpit area). Depending on the size of the tumor, the cancer stage and other factors, the doctor may recommend mastectomy surgery to remove the entire breast.

In addition to surgery, patients may be treated with a combination of the following breast cancer therapies.

Radiation therapy for breast cancer: Luminal B cancer tumor features are particularly prone to late recurrence, which is the return of the cancer more than five years after it was diagnosed and treated. Radiation therapy is often given to women after breast-conserving surgery and sometimes after mastectomy surgery. It is used to help destroy any potential remaining cancer cells and reduce the chances of the cancer returning locally later (recurrent breast cancer).

Chemotherapy for breast cancer: If luminal B is HER2-positive (HER2+), patients with early-stage and locally advanced breast cancer may be treated with chemotherapy drugs both before surgery to help shrink the tumor or after surgery to help destroy any remaining cancer cells. Chemotherapy drugs may also be used if luminal B is HER2-negative. A gene expression test helps the doctor determine how well HER2-negative luminal B may respond to the treatment and if there is a benefit to receiving chemotherapy, as not everyone may benefit.

Hormone therapy for breast cancer: Since luminal B is estrogen receptor-positive, meaning the cancer cells grow and thrive using estrogen, patients are typically given drugs to help block these estrogen receptors or reduce levels of the hormone in the body. This is called hormone therapy, and it is usually given for a minimum of five years. Some research reveals that taking hormone therapy for up to 10 years may benefit patients diagnosed with breast cancers that tend to recur later.

Targeted drug therapy for breast cancer: Certain drugs are used to target and block the different molecular components of luminal B that support the cancer’s growth. These targeted drug therapies include the drug Verzenio^® (abemaciclib), which is approved by the U.S. Food and Drug Administration for use (along with hormone therapy) for cancer cells that are HER2-negative and estrogen receptor-positive. It is also approved for patients whose luminal B cells have higher levels of the Ki-67 protein.

Immunotherapy for breast cancer: Targeted drug therapy may also be combined with immunotherapy to help the body’s own immune system fight cancer. For instance, patients with HER2+ luminal B may be given laboratory-made proteins called monoclonal antibodies that resemble the immune system’s naturally made antibodies. They attach to HER2 and help block it in order to reduce cancer cell growth.

Metastatic luminal B breast cancer that has spread to distant sites in the body like the lungs, liver or brain (Stage 4) are also treated with a combination of chemotherapy, radiation therapy, targeted drug therapy and hormone therapy. Patients with Stage 4 breast cancer are given treatment options that aim to reduce the amount of cancer in the body and relieve symptoms like pain and discomfort to help improve their quality of life.

Luminal B Breast Cancer Prognosis

Luminal B breast cancer is slightly harder to treat than luminal A (the most common subtype of the disease).

The overall five-year relative survival rate for women diagnosed with luminal B breast cancer between 2014 and 2020 was 91.5%, according to the National Cancer Institute (NCI) SEER (Surveillance, Epidemiology, and End Results) Program. It was 95.1% for women diagnosed with luminal A breast cancer.

During this same timeframe, luminal B’s survival rate by stage was:

• 99.3% for local-stage cancer that had not spread outside the breast
• 90.4% for regional-stage cancer that had spread to area lymph nodes
• 45.8% for distant-stage cancer that had spread to organs or structures in other parts of the body

While the overall prognosis for luminal A is slightly better than for luminal B, women diagnosed at the distant stage had a higher chance of recovery with luminal B.

Men — who may be diagnosed with breast cancer at a more advanced stage than women — had an overall five-year relative survival rate of 65.1% for the disease, according to an analysis of NCI SEER data from 2014 to 2017 in Breast Cancer Research.

Clinical trials are being conducted to help discover new breast cancer treatments. For example, therapies are being studied to counter a cell growth-promoting protein called wild type RAS that is commonly overactivated in luminal B cancer cells.

Breast Cancer Care and Research at City of Hope

At City of Hope, researchers and clinicians work together closely to provide patients access to breast cancer clinical trials and newly developed therapies aimed at improving survival outcomes for each individual. Comprehensive luminal B cancer care includes innovative radiation therapy, targeted drug therapy, hormone therapy, chemotherapy and advanced surgical techniques.