A Need-to-Know Guide to HER2-Positive Cancer

If you or a loved one is diagnosed with cancer, you already have a lot going through your mind. You will likely hear medical terminology you've never encountered before, and after getting some news that's overwhelming enough on its own, it can be hard to sit calmly for a doctor's explanation. One of the most common terms related to cancer is HER2, which is a meaningless abbreviation on the surface. Let's take a look at what it means and how it affects treatment.

What Does HER2 Mean?

HER2-positive tumors are associated with up to 20 percent of breast cancer cases, and research has indicated that they can also be associated with bladder, pancreatic, stomach, and several other cancer types. So, what exactly is HER2? The Annals of Oncology explains that the abbreviation refers to a protein called "human epidermal growth factor receptor-2," which controls cell growth. Sometimes, a person with cancer has too much of this protein or too many copies of the HER2 gene, which controls the production of the protein. This causes cancer cell growth to accelerate. When cancer cells show excess HER2 protein, the cancer is thus categorized as HER2-positive, and because of that accelerated cell growth, HER2 cancers tend to be more aggressive.

Treatment for HER2

While the HER2 protein encourages rapid cancer growth, it can be targeted in treatment. Targeted cancer therapies seek out specific molecules on which to act, rather than acting on all rapidly dividing cells in the way chemotherapy does. Many of these targeted therapies work to prevent tumor cell growth rather than killing existing tumor cells. This approach helps to minimize damage to healthy cells, and the side effects are often different as a result. For some people, they're milder than the side effects of chemotherapy.

Targeted therapies, also referred to as "precision medicine," are the focus of much current cancer treatment and prevention research. So far, there are four agents approved for treatment of HER2-positive breast cancer:

1. Trastuzumab is often used for early-stage and metastatic breast cancer that's HER2-positive. The side effects of trastuzumab are usually mild, including joint pain, hot flashes, nausea, and vomiting. This agent is administered by IV in a similar manner to chemotherapy. Trastuzumab can reduce the risk of recurrence by as much as half in HER2-positive tumors.
2. Pertuzumab, provided as an alternative to (or in conjunction with) trastuzumab, is also administered by IV.
3. Ado-trastuzumab emtansine is prescribed for people with advanced disease who have already been treated with trastuzumab. It is also administered by IV as a part of a chemotherapy regimen.
4. Lapatinib is delivered in pill form and is often prescribed if it appears that trastuzumab has stopped working. The side effects of lapatinib include hand-foot syndrome, which may cause blistering and peeling of the hands and feet, as well as severe diarrhea.

Trastuzumab, pertuzumab, and ado-trastuzumab emtansine all increase the risk for heart problems, particularly if the patient is predisposed to heart issues or has already received another treatment that increased their risk. As a result, heart function needs to be routinely monitored during and after treatment.

There are some limitations to targeted therapies: The cancer may find other ways to fuel growth independent of the HER2 protein, so the therapy will have less impact, or the protein may mutate, making it resistant to the targeted therapy. This is one of the reasons targeted therapies are often used in concert with traditional chemotherapy. There is no benefit, however, to therapies targeting the HER2 protein in people who are not overexpressing that protein. Note also that these therapies should not be prescribed to pregnant women.

Perhaps more important than being knowledgeable of what HER2 means is being aware of how targeted therapies work. If you or a relative is diagnosed with HER2-positive cancer, it's best that you fully understand your medical team's response. While these cancers tend to grow quickly, targeted treatment may provide an effective treatment plan and an encouraging prognosis as part of overall cancer treatment protocol.