10 Facts About HER2-Positive Breast Cancer

by Lara DeSanto Health Writer

A breast cancer diagnosis can be complicated because there are several kinds, each behaving differently and requiring targeted treatment approaches. One of the main types, which can be more aggressive and grow faster than the others, is called HER2-positive breast cancer; it accounts for 25% of all breast cancers. Here, we’ll share 10 key facts about this type—from diagnostic tests to various treatment methods—to help simplify the decisions you or a loved one must make after receiving a HER2-positive diagnosis.

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HER2 Is a Protein That Accelerates Cell Growth

First, what do those letters mean? HER2 stands for human epidermal growth factor receptor 2, which is a gene that makes HER2 proteins, according to the National Institutes of Health. HER2 proteins are normally found on the surface of healthy breast cells to promote breast cell growth and repair, but when HER2 mutates, things go wrong. “An excess of HER2 proteins causes cells to grow fast. When cancer cells have more HER2, this causes cancer cells to grow more rapidly,” explains Swati Kulkarni, M.D., a breast surgeon at Northwestern Memorial Hospital in Chicago.

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HER2-Positive Breast Cancer Develops From a Gene Mutation

A common and difficult question after a cancer diagnosis is: Why did this happen? With HER2-positive breast cancer—and other breast cancers, too—the answer is not a simple one. That said, research does show that HER2-positive breast cancer develops from a mutation in the HER2 gene leading to acceleration of cell growth. We just don’t know why the mutation happens. What’s clear is that it’s not a cancer gene that can be passed down from parent to child, according to Moffitt Cancer Center—both the mutation and subsequent cancer likely develop from a combination of genetic, environmental, and lifestyle factors.

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There Are Known Risk Factors for HER2-Positive Breast Cancer

Again, while exact cause is difficult to pinpoint, researchers have identified some risk factors for HER2-positive disease, according to Moffit Cancer Center. For example, being a higher weight, not living an active lifestyle, having a child for the first time after age 30, and using tobacco products can up your risk. This cancer is also more likely to occur in younger women, adds Brian Czerniecki, M.D., chair of the department of breast oncology at Moffit Cancer Center in Tampa, FL. According to one 2020 study, 22.63% of younger women (defined here as under 40) had HER2-positive breast cancer compared with 13.41% of older women.

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HER2-Positive Breast Cancers Can Be Aggressive

One way in which HER2-positive breast cancers are unique from other breast cancers is that they tend to be more aggressive, says Dr. Czerniecki. “The HER2 receptors get massively overexpressed, and they drive the cell to unbelievable growth, and that can lead them to leave the inside of the duct and either grow into the fat or travel to the lymph nodes or bone marrow,” he says. Because of this, these cancers tend to spread sooner and have a higher recurrence risk, he adds.

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Diagnosis of HER2-Positive Breast Cancer Involves a Series of Tests

After you get a general diagnosis of breast cancer—usually after a mammogram—the next step is to determine which type it is, explains Dr. Kulkarni. That involves further testing of a tissue sample taken during a tumor biopsy, including tests that determine the presence of proteins like HER2. In HER2 testing, your tumor gets a score of 0, 1+, 2+, or 3+. “Zero and 1+ are considered negative, and 3+ is considered positive,” she clarifies. If you get a +2 score, further testing called fluorescence in situ hybridization (FISH) helps determine whether your cancer is HER2-positive.

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Advancements in HER2-Positive Treatments Provide Effective Options

Despite their aggressive nature, HER2-positive breast cancer tumors are easier to treat than ever, thanks to advances in treatment research. “It’s one of the biggest success stories in breast cancer, because we have developed a whole host of effective therapies that target HER2,” says Dr. Kulkarni. “We turned a very aggressive type of breast cancer into something we can treat with many options.” So although it can be frightening to receive a diagnosis of this more aggressive breast cancer, know that there are effective therapies available, she says. More on those, next.

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HER2-Positive Treatment Options Are Given in Combinations

There are four main breast cancer treatments: Surgery and radiation (local treatments), and chemotherapy and targeted therapy (systemic treatments), Dr. Kulkarni says. “The stage of HER2-positive disease can help determine the order in which these four treatments are given.” Classically, people have surgery first—but with HER2-positive breast cancer, you may have systemic treatments first to shrink the tumor, which can lead to less extensive surgery later. If the tumor disappears completely prior to surgery—which is common—there’s a 90% chance of not having a recurrence, adds Dr. Czerniecki. “That translates into a pretty good long-term chance of survival.”

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Targeted Therapies for HER2-Positive Breast Cancer Increase Survival Rates

The newest of those four main treatments are effective drugs that specifically target the HER2 protein, says Dr. Kulkarni. There are three main types of targeted drugs for HER2, according to the American Cancer Society: Monoclonal antibodies, antibody-drug conjugates, and kinase inhibitors. They all work in different ways to attack the HER2 protein in your cancer cells and can be used in combination with other treatments, like chemo. The first to be approved has increased survival rates for women with stage 1-3 HER2-positive breast cancer more than 30%, according to the National Cancer Institute.

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More HER2-Positive Treatments Are on the Horizon

Scientists are working away to continue improving treatment options for HER2-positive breast cancer. For example, since there’s a higher risk of recurrence with these cancers, there are clinical trials in process for vaccines to help prevent this from happening, says Dr. Czerniecki. Another big research focus is on treatments for people with metastatic (spreading) HER2-positive breast cancer. “They become resistant to the existing therapies over time, so a lot of what we’re working on is how to help those people, and come up with therapies for them that helps to overcome resistance,” he explains. “We still have work to do.”

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It's A Hopeful Time for HER2-Positive Breast Cancer

If you or a loved one are diagnosed with this cancer, remember this: There are more effective treatments available than ever. “The big take-home point about HER2-positive tumors is that while this is very aggressive tumor, these very targeted treatments are incredibly effective,” Dr. Kulkarni says. So while prognosis used to be poor, with the introduction of targeted treatments and more to come, people see much better outcomes, she says. “It’s very exciting times for HER2-positive breast cancer research,” Dr. Czerniecki says.

Lara DeSanto
Meet Our Writer
Lara DeSanto

Lara is a former digital editor for HealthCentral, covering Sexual Health, Digestive Health, Head and Neck Cancer, and Gynecologic Cancers. She continues to contribute to HealthCentral while she works towards her masters in marriage and family therapy and art therapy. In a past life, she worked as the patient education editor at the American College of OB-GYNs and as a news writer/editor at WTOP.com.