HER2 status is an important piece of information when deciding how to treat metastatic breast cancer. HER2, or “human epidermal growth factor receptor 2,” is a protein the body uses to grow and repair breast tissue. Some breast cancers produce excess amounts of HER2 proteins. These proteins are located on the outside of cancer cells and attract growth hormones that the cancer cells can use to promote their growth, division, and spread.
Healthcare providers can order tests to determine if breast cancer is HER2-positive. These tests involve taking a sample of breast cancer cells, which are then examined in a lab.
There are a number of cancer drugs that can target cancer cells that are HER2-positive. These drugs are referred to as targeted therapies and are potential treatment options for HER2-positive metastatic breast cancer.
Here, we will look at how targeted therapies work to treat metastatic breast cancer (MBC) that is HER2-positive.
Biomarkers
HER2 proteins are one example of a cancer biomarker. Cancer biomarkers are molecules that are produced by cancer cells, or by the body in response to the presence of cancer cells. Targeted therapies are drugs that identify and act on cells with a particular biomarker.
Types of targeted therapy for MBC
Different targeted therapy drugs work in different ways. There are several types of targeted therapy drugs that can be used to treat HER2-positive MBC:
- Monoclonal antibodies are synthetic versions of antibodies that occur naturally in the body. They work by attaching to HER2 proteins to block or prevent these proteins from attracting growth hormones. This prevents the cancer cells from dividing, growing, and spreading.
- Antibody drug conjugates (ADCs). Some drugs include a combination of monoclonal antibodies and other anti-cancer drugs—such as chemotherapy agents or topoisomerase inhibitors (which work by blocking an enzyme that cancer cells need to replicate DNA). These are called antibody drug conjugates or ADCs. In addition to inhibiting cancer cells from using HER2, ADCs also release anti-cancer drugs directly into HER2-positive cancer cells.
- Tyrosine kinase inhibitors (TKIs). Tyrosine kinase are enzymes that cells need to grow, divide, and signal other cells. Certain cancer cells produce excess levels of these enzymes. TKIs work by blocking these enzymes, preventing cancer cells from growing and dividing. These drugs may be given when cancer has progressed during initial treatment.
Targeted therapies can also be used in combination with other therapies, including chemotherapy, endocrine therapy, immunotherapy, and other targeted therapies.
Making treatment decisions
It is important to remember that every case of MBC is different, that treatment is an ongoing process, and there are many factors to consider when making treatment decisions. Targeted therapies can be effective against HER2-positive MBC, but also come with a risk of side effects, and some of those side effects can be serious. The best thing a person with MBC can do is work closely with a healthcare team to understand their treatment options, how those treatment options work, and how a therapy aligns with treatment goals.
