What Is HER2-Positive Metastatic Breast Cancer?

There are many many types (and subtypes) of breast cancer. Here’s how to decode one diagnosis.

November 29, 2023

her2 positive metastatic breast cancer illustration

One of many overwhelming parts of being diagnosed with breast cancer: Realizing just how many types—and subtypes—of breast cancer exist. If you or someone you love has been diagnosed with HER2-positive metastatic breast cancer (sometimes referred to using the code-like abbreviation “HER2+ MBC”) the name alone is a lot to process.

What is HER2-positive metastatic breast cancer?

To break it down: The first part of the name, HER2, stands for “human epidermal growth factor receptor 2.” This refers to a protein found on the surface of breast cells that helps direct how quickly those cells grow and divide. Having HER2-positive breast cancer (also written as “HER2+ breast cancer”) indicates that your breast cells contain an elevated amount of this HER2 protein, which can lead those cells to grow and divide too quickly, resulting in tumors and/or cancer. Since the symptoms of this type of breast cancer are the same as you’d experience with many other types of breast cancer, a biopsy is the only way to know that you’re HER2-positive; about 20% of breast cancer cases are.

Now for the second part of that hefty name: metastatic breast cancer. An added challenge that comes with an HER2-positive breast cancer diagnosis is that this type of cancer tends to be aggressive and spread quickly. In about half of cases, by the time it’s diagnosed, HER2-positive cancer has already progressed to being metastatic breast cancer—abbreviated as MBC (also called stage IV breast cancer, or advanced breast cancer). Metastatic means that cancer has spread beyond the breast to other parts of the body, like your lymph nodes, bones, brain, or other organs, and that the disease can no longer be completely cured but merely paused, slowed, and managed. Even when HER2-positive breast cancer is discovered as early-stage cancer and treated into remission, it often comes back later in the form of metastatic breast cancer because it’s an aggressive cancer.

HER2-positive metastatic breast cancer symptoms

When you have HER2-positive breast cancer, you will notice the same symptoms that people with most other forms of breast cancer will spot. These may include a new lump you feel in your breast, a mass found during a mammogram, a change in breast shape, clear or bloody nipple discharge, breast swelling, and changes to the skin on your breast. The risk factors for HER2-positive breast cancer also look the same as those for other breast cancers: Having an inherited gene mutation like BRCA1 or BRCA2, starting your menstrual cycle at an early age, and high alcohol consumption are all factors that could increase your chances of having this disease.

HER2-positive metastatic breast cancer treatment

What is different—in an optimistic way—about being diagnosed with HER2-positive breast cancer versus HER2-negative breast cancer is that you have options beyond the standard first-line metastatic breast cancer treatments like chemotherapy drugs, surgery, and radiation. In addition to those, your oncologist can employ targeted treatments that interfere with HER2 proteins. These include IV infusions or injections of monoclonal antibodies or of drugs called tyrosine kinase inhibitors (TKIs). Another category of anti-HER2 therapy is antibody-drug conjugates (ADCs). These breakthrough treatments employ cancer-seeking antibodies with potent cancer drugs attached, to help those drugs stealthily enter cancer cells and shut them down without harming healthy cells or causing the serious side effects associated with systemic therapies like chemotherapy drugs. Studies show that ADCs have contributed to a significant improvement in overall survival rates for HER2-positive breast cancer patients with metastatic disease.

Another factor that plays into how HER2-positive metastatic breast cancer is treated: whether breast cancer cells are hormone-receptor positive—meaning certain hormones are helping the cancer to grow. About half of HER2-positive cancers have hormone receptors. If you’re HER2-positive and your cancer cells also have estrogen receptors (ER positive) or progesterone receptors (PR positive), your breast cancer is what’s called double-positive. If, more rarely, HER2-positive breast cancer cells have receptors for both estrogen and progesterone, that’s known as triple-positive breast cancer. Being hormone-receptor-positive means your breast cancer treatments can include endocrine therapy, using drugs that prevent the body from producing the specific hormones that are helping cancer grow and spread. Thanks to these treatments, five-year survival rates for people with HER2-positive metastatic breast cancer who are hormone-receptor positive are slightly higher than those who are negative.

The goal in the treatment of metastatic breast cancer is progression-free survival while maintaining quality of life. You’ll need to undergo regular blood tests and scans to be sure that your cancer has not grown or spread. Despite the rapid advances being made when it comes to the treatment of patients with HER2-positive metastatic breast cancer, which have led to an improved outlook for survival rates, patients still develop resistance to therapies over time and you may experience disease progression. It’s important to follow up with your health care provider if you notice new changes in your breasts or your body, or develop any kind of new symptom, as these may be signs that your breast cancer has spread and that your treatment plan needs to be adjusted. As a later-line treatment option, people with HER2-positive breast cancer often have opportunities to participate in a clinical trial, which gives you access to promising treatments that haven’t yet been FDA-approved and also allows you to be part of the process of finding the next breakthrough in breast cancer research.

After an HER2-positive metastatic breast cancer diagnosis, what’s next?

When you’re diagnosed with HER2-positive metastatic breast cancer, processing all of the available information and treatment options at once is challenging. Do your best to practice self-care and stay positive, work on understanding your treatment options one step at a time, and keep a running list of questions to ask your oncologist or other health care provider at your next visit. To get you started, here are seven questions to ask your doctor when you’re diagnosed with metastatic breast cancer. To find out more about what to expect when you have HER2-positive metastatic breast cancer, read one woman’s firsthand account of her diagnosis, as told to Glamour, and visit our metastatic breast cancer page for more personal stories and updates on efforts to find new treatments and a cure.