What You Should Know About Metastatic Breast Cancer (MBC)

What You Should Know About Metastatic Breast Cancer (MBC) What You Should Know About Metastatic Breast Cancer (MBC)

By: Matthew Wright, MDMegan Kruse, MD • Posted on February 18, 2021

What is Metastatic Breast Cancer?

Metastatic Breast Cancer (MBC) occurs when cancer that has originated in the breast has traveled to a distant part of the body.

Different types of breast cancer

There are different types of breast cancer that are categorized according to the hormone/growth factor/biomarker status and microscopic appearance.

  1. Hormonally driven breast cancers are fueled by estrogen and/or progesterone and are designated as estrogen receptor positive and progesterone receptor positive, respectively.
  2. Breast cancer that is supplied by overexpression of a cellular protein named HER2 (or HER2/neu) is referred to as HER2 positive.
  3. Breast cancer that is not driven by any of these three is designated as triple negative breast cancer.

This important classification is necessary to determine the optimal recommended treatment.

The 2 most common types of breast cancer

The two most common types of breast cancer classified according to their microscopic appearance are:

  1. Invasive Ductal Carcinoma (IDC)
  2. Invasive Lobular Carcinoma (ILC)

What Treatments are Available for MBC?

Unfortunately, MBC is ultimately incurable, but more recent treatment options have led to improved survival rates that can last several years. Women with MBC can lead full lives.

The disease becomes more life-threatening typically when it impairs vital organs such as the heart, lungs, liver and brain.

Systemic therapy

Treatments for MBC generally consist of systemic therapy, meaning treatment that permeates throughout the entire body to attack cancer cells anywhere in the body.

Treatments for estrogen receptor-positive (ER-positive) MBC

For estrogen receptor-positive (ER-positive) MBC, treatment consists of endocrine therapy (formerly known as hormonal therapy). This treatment includes medications that either directly or indirectly block the estrogen that is fueling the cancer growth.

Examples of endocrine therapy

  • Aromatase Inhibitors (AIs) - such as anastrozole (Arimidex®), letrozole (Femara®) and exemestane (Aromacin®). AIs can affect the bone and the joints.
  • Tamoxifen - an estrogen agonist/antagonist that can stimulate the lining of the uterus (endometrium), so any vaginal bleeding needs to be evaluated.
  • Fulvestrant (Fasolex®) - an estrogen receptor antagonist.
  • CDK inhibitors - such as palbociclib (Ibrance®), ribociclib (Kisqali®) and abemaciclib (Verzenio®). CDK inhibitors are cyclin-dependent kinase inhibitors that target the CDK4 (cyclin D1) and CDK6 (cyclin D3) cell pathways.

Because the ovaries are the main source of estrogen in premenopausal women, menopause is often induced via surgery or medications. Genetic testing for mutations in DNA (inherited or developed in the cancer itself) plays an important role in opening up treatment options for patients with MBC.


An additional treatment option for ER positive, HER2 negative MBC targets a specific mutated protein that contributes to cancer growth. This alteration is a PIK3CA mutation and the targeted treatment is alpelisib (Picray®).

Treatments for HER2 positive MBC

HER2 positive MBC treatment includes:

  • Chemotherapy - docetaxel (Taxotere®)
  • HER2-targeted therapy - trastuzumab (Herceptin®), pertuzumab (Perjeta®), ado-trastuzumab emtansine (Kadcyla®) or TDM-1, tucatinib (Tukysa®)

Treatments for triple negative MBC

Potential treatment options for triple negative MBC are:

  • Immunotherapy - atezolizumab (Tecentriq®), pembrolizumab (Keytruda®)
  • Targeted Therapy - PARP inhibitors like olaparib (Lynparza®) for patients with BRCA mutations
  • Chemotherapy - nab-paclitaxel (Abraxane®), doxorubicin (Adriamycin®), capecitabine (Xeloda®), eribulin (Halaven®)

Risks, benefits and side effects of each treatment should be discussed with your physician before starting therapy.

Targeted radiation therapy may be recommended for focal areas where the cancer has spread to the bones or brain. Another treatment for metastatic bone disease that targets bone destruction includes bisphosphonates (zolendronate (Zometa® or Reclast®) or denosumab (Prolia®), typically given in conjunction with supplemental calcium and vitamin D. Bisphosphonates and denosumab are common medications usually well tolerated and used in postmenopausal women to treat osteoporosis.

In women who are receiving therapies to reduce estrogen in the body, many times there can be bone loss and the lack of sex hormones can cause vaginal dryness and bladder irritability. There are several treatment options for bone loss and there are options for women with Genitourinary Syndrome of Menopause (GSM).

Tips for Living With MBC

A cancer diagnosis as well as the stress of treatment can take a negative toll on a person's mental and physical health, but MBC doesn’t have to dominate your life.

In order to optimize your health, all individuals should strive to:

Be Strong, Be Healthy, Be in Charge!

Matthew Wright, MD and Megan Kruse, MD

Matthew D. Wright, MD is a second year Hematology Oncology fellow at the Taussig Cancer Center at the Cleveland Clinic. He earned his medical degree from Georgetown University School of Medicine. He completed his residency at Case Western Reserve University/University Hospitals.

Megan Kruse, MD is a Breast Medical Oncologist at the Taussig Cancer Institute of Cleveland Clinic. She received her MD from Case Western Reserve University in Cleveland, OH and completed her residency in Internal Medicine at the University of Pittsburgh Medical Center. She then completed Hematology & Medical Oncology fellowship at Cleveland Clinic where she served as Chief Fellow and was appointed as Associate Staff in 2017. Her main area of clinical investigation is optimizing care for patients with lobular breast cancer. She also has an interest in medical education and serves as the Associate Program Director of the Hematology/Oncology Fellowship at Cleveland Clinic.

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