Thanks to research and clinical trials, people with HER2-positive breast cancer now have more effective treatment options available. Advances in cancer care are leading to better outcomes and survival rates for people with this breast cancer subtype.

Approximately 20 percent of people with breast cancer have HER2-positive tumors. HER2 stands for human epidermal growth factor receptor 2, also called the HER2 gene. This gene makes the HER protein, which influences tumor cell growth. It also gives researchers something to target when developing more effective treatment strategies.

If you have this type of breast cancer, knowing what your treatment options are and how they work can help you make informed decisions about your health. Keep reading to learn six facts about HER2-positive breast cancer treatment.

1. Monoclonal Antibodies Are Medications That Recognize and Attack HER2 Proteins

Antibodies are proteins. The immune system makes these proteins to help protect the body from things that shouldn’t be roaming inside, like bacteria, viruses, and cancer cells. Antibodies can tell the difference between normal cells and foreign invaders by reading unique markers, or antigens.

Antigens are usually proteins or sugars. They attach to cells, viruses, and other substances and can communicate what’s inside. When an antibody recognizes an antigen that shouldn’t be there, it attaches to the antigen and destroys it with the help of the rest of the immune system.

Not all antibodies will attach to all antigens. They circulate throughout the bloodstream, only stopping when they find a specific antigen. Imagine having a bowl of colored candies in front of you. You’re told you can only eat the yellow ones. Although they are all the same shape and size and are all in a bowl together, you start picking out and eating the yellow ones, leaving the rest alone. The antibody-antigen relationship is similar.

Monoclonal Antibodies and HER2 Proteins

Monoclonal antibodies are made in a laboratory. They play the same role as natural antibodies, but researchers create them to attach to a specific target — like the HER2 protein. If you have HER2-positive breast cancer and your oncologist recommends trying a monoclonal antibody, they will prescribe one that can attach to the HER2 protein on breast cancer cells and stop those cells from growing.

Anti-HER2 monoclonal antibodies that can recognize and attack the HER2 protein include:

• Margetuximab-cmkb (Margenza)
• Pertuzumab (Perjeta)
• Pertuzumab, trastuzumab, and hyaluronidase-zzxf (Phesgo)
• Trastuzumab (Herceptin)
• Trastuzumab-dkst (Ogivri)
• Trastuzumab and hyaluronidase-oysk (Herceptin Hylecta)

Which monoclonal antibody your oncologist recommends will depend on your breast cancer diagnosis and treatment plan. Herceptin, for example, can treat both early-stage breast cancer and advanced breast cancer. Margenza is often used with chemotherapy to treat advanced breast cancer, and only after two other HER2 treatments have been tried.

Some monoclonal antibodies are given intravenously (through a vein) at a hospital or clinic. Others, like Phesgo, can be given subcutaneously (under the skin) at your doctor’s office in just a few minutes. If you have questions about monoclonal antibodies or their potential side effects, talk to your cancer care team.

2. Targeted Therapies Block the Growth of Cancer on a Molecular Level

Targeted therapies are treatments that recognize and destroy specific targets — in this case, HER2-positive breast cancer cells. When you were diagnosed, you likely had a biopsy followed by two tests to determine your HER2 status: immunohistochemistry (IHC test) and fluorescence in situ hybridization (FISH) testing. Knowing your HER2 status is important because targeted drugs are not used to treat HER2-negative breast cancers.

Targeted therapies block the growth of cancer on a molecular level. They do this by turning off or interfering with signals that tell cancer cells to grow and divide. Targeted therapies can deliver toxins to the cancer cells while avoiding normal, healthy cells. They can also change the proteins within cancer cells, causing the cells to die. Some can block the growth of new blood vessels that may feed cancer cells. This type of therapy is often called precision medicine because its targets are so specific.

Monoclonal antibodies are targeted drugs, as are kinase inhibitors and antibody-drug conjugates.

Kinase Inhibitors Are Administered as a Pill

Kinase inhibitors stop a type of protein called a kinase from doing its job. HER2 is a kinase. So, kinase inhibitors target HER2 proteins and block them from telling the breast cancer cells to grow and multiply.

Kinase inhibitors used to treat HER2-positive breast cancer include:

• Neratinib (Nerlynx)
• Tucatinib (Tukysa)
• Lapatinib (Tykerb)

These drugs are pills that you take orally (by mouth).

Antibody-Drug Conjugates Are Administered Intravenously

An antibody-drug conjugate (ADC) is targeted therapy plus chemotherapy. The monoclonal antibody attaches to the HER2 protein on the breast cancer cell and acts as a beacon, helping the chemotherapy drug find and destroy it.

Antibody-drug conjugates used to treat HER2-positive breast cancer include:

• T-DM1 or ado-trastuzumab emtansine (Kadcyla)
• Fam-trastuzumab deruxtecan-nxki (Enhertu)

These drugs are administered intravenously.

3. Surgery Removes Cancerous Tissue

Surgery is a common treatment for many types of breast cancer, including HER2-positive. The two primary surgeries to remove cancerous breast tissue are:

• Breast-conserving surgery (lumpectomy, quadrantectomy, and partial mastectomy) — Removal of the tumor and a small part of the breast
• Mastectomy — Removal of the entire breast

Your health care provider should explain which surgery they recommend and why. If you have a follow-up operation to reconstruct or repair your breast once the cancer has been removed, it’s called reconstructive surgery.

Some people with HER2-positive breast cancer also need to have lymph nodes removed. Because HER2-positive breast cancer is likely to grow fast and spread (metastatic breast cancer), your doctor may want to take a closer look at your lymph nodes to determine whether cancer cells have spread beyond the breast. This can be done during the main surgery or as a separate operation.

4. Radiation Therapy May Reduce the Chance That a Tumor Returns

Your oncologist might recommend radiation therapy if there’s a high risk of your HER2-positive tumor returning. Radiation therapy damages cancer cells using high-energy rays. The two types of radiation most often used to treat breast cancer are external beam radiation therapy and brachytherapy. Which type you need, when, and how often will depend on the size of the tumor, whether lymph nodes are involved, and other factors.

Radiation can be given at the same time as targeted therapy and hormone therapy. Studies have shown that a combination of surgery, targeted therapy, and radiation can be an effective treatment strategy for HER2-positive breast cancer.

5. Chemotherapy May Help Kill Cancer Cells

Chemotherapy is another treatment option your oncologist may recommend. It works by attacking cancer cells as they divide, preventing them from growing, splitting, and making more cells.

While targeted therapy works by destroying specific cancer cells, chemotherapy will destroy any type of cancer cell. Without a target, it sometimes kills healthy cells. Your oncologist should explain the potential side effects before you start a chemo regimen.

When used to treat HER2-positive breast cancer, chemotherapy medications may be combined with other treatments, like a monoclonal antibody, kinase inhibitor, or both.

6. Hormone Therapy May Be Used To Block Hormones and Starve Cancer Cells

If your HER2-positive breast cancer is also hormone receptor-positive, your oncologist could recommend hormone therapy (also called endocrine therapy).

A hormone receptor-positive tumor responds to estrogen, progesterone, or both. When these hormones attach to hormone receptors on the breast cancer cells, the cells are more likely to grow and spread. Some hormone therapies work by attaching to the hormone receptor first, effectively blocking the hormone from attaching. Others starve cancer cells by lowering the estrogen levels in the body.

Hormone therapy can be used as neoadjuvant therapy (before surgery) or as adjuvant therapy (after surgery). According to the American Cancer Society, when hormone therapy is used as an adjuvant treatment, the goal is to reduce the risk of the cancer recurring (coming back) after surgery.

Several HER2-positive breast cancer treatments are currently available. Treatment options will likely expand and improve as clinical trials continue to develop new therapies. Ask your oncologist which treatment option they recommend for you and why. If there’s ever anything you don’t understand about your breast cancer treatment plan, ask your care cancer team to explain it until you do.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 69,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you undergone treatment for HER2-positive breast cancer? Are you in treatment now? Share your experience in the comments below, or start a conversation by posting on your Activities page.