What to Expect After a HER2-Positive Metastatic Breast Cancer Diagnosis

Understanding what it means to be diagnosed with HER2-positive metastatic breast cancer (sometimes called “HER2+ MBC” or “HER2+ breast cancer”) can feel like riding a roller coaster. Amid the initial shock and fear that accompanies any cancer diagnosis, there’s another low that comes when your oncologist tells you that this specific type of breast cancer tends to be aggressive and spread quickly. The reason lies in the “HER2-positive” part of its name: That term indicates that your breast cells have an excess of proteins called HER2 (short for “human epidermal growth factor receptor 2”), which are in charge of cell growth and division—and, of course, cells growing and diving too quickly is what leads to tumors.

That said, the real stomach-dropping, devastating moment is being told that your HER2-positive breast cancer is metastatic, also known as MBC, stage IV, or advanced breast cancer. This means the disease has already spread significantly—beyond the breast to other parts of the body, such as your bones, brain, or other organs. Unlike early-stage cancer, metastatic breast cancer can’t be cured—regardless of HER2 status (whether you’re HER2 positive or HER2 negative). However, there are many breast cancer treatments that may be able to pause or significantly slow your disease progression while allowing you to maintain a high quality of life.

That’s where the news of a HER2-positive diagnosis takes an unexpectedly optimistic turn: Treatment options are more plentiful for breast cancer patients designated as HER2-positive. In fact, among all the types of breast cancer, HER2-positive breast cancer has one of the longest lists of effective treatment options. The reason goes back to those HER2 proteins. You’ll be able to take advantage of highly targeted breast cancer treatments that work by specifically interfering with these cell-growth proteins, thus slowing the spread of cancer cells, without much harm to healthy cells or the lifestyle-altering side effects that other systemic treatments like chemotherapy are known for. Your oncologist may refer to these targeted treatments as “anti-HER2 therapies” or “HER2-targeted agents”.

There are a few different types of HER2-targeted agents. One main category of HER2 therapies is monoclonal antibodies (which come with unpronounceable names like pertuzumab, trastuzumab, and margetuximab). These are administered in a healthcare setting via IV infusions or injections. Monoclonal antibodies have proven to be a highly effective tool in curing early breast cancer that’s HER2-positive, but they’re also used when managing metastatic disease over the longer term. The standard of care for treatment of patients with HER2-positive metastatic breast cancer is usually to administer monoclonal antibodies in combination with chemotherapy (commonly used drugs include capecitabine, or a category called taxanes, which includes drugs like docetaxel) and/or surgery as a first-line treatment. Depending on your response rate, your doctor will then adjust your combination of therapies as time goes on.

A second type of systemic therapy your oncologist may talk about—and another option that’s useful only for HER2-positive breast cancer—is tyrosine kinase inhibitors (TKIs). A tyrosine kinase is a category of protein that includes those HER2 proteins; within cells, their job is to relay messages and act as a receptor. TKIs (which have more of those fun drug names: tucatinib, neratinib, lapatinib) interfere with that messaging—so in the case of HER2-positive breast cancer, they keep HER2 proteins from telling cancer cells to grow and divide. TKIs come in the form of pills taken once or twice a day.

A more recent breakthrough in the treatment of HER2-positive breast cancer is a category known as antibody-drug conjugates (ADCs), which are therapies that combine antibodies with a potent anti-cancer drug. Examples include trastuzumab deruxtecan, trastuzumab emtansine (also called T-DM1 or ado-trastuzumab emtansine). When these combination treatments, given by IV, enter the body, the antibodies seek out  breast cancer cells and bind to their HER2 proteins, at which point the linked anti-cancer drug can be efficiently absorbed. This targeted process allows antibody-drug conjugates to eliminate cancer cells with minimal harm to healthy cells. The first ADC was FDA-approved for the treatment of HER2-positive metastatic breast cancer in 2013, and others have since been introduced and approved for treatment of patients with metastatic disease, with more in the research pipeline today. Studies show that ADCs have contributed to a significant improvement in overall survival rates for metastatic HER2-positive breast cancer patients.

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