If you or a loved one has been diagnosed with breast cancer, you may be wondering what HER2 is. You also may be wondering what it means to have HER2-positive or HER2-negative breast cancer.

This acronym, which stands for human epidermal growth factor receptor 2, is one indicator. Estrogen and progesterone hormones can also determine the pathology of your specific breast cancer. Your HER2 status can also help determine how aggressive the cancer is. Your doctor will use this information to evaluate your treatment options.

In recent years, there have been significant developments in the treatment of those who have HER2-positive breast cancer. This has resulted in a better outlook for people with this condition.

HER2 is a protein created by the HER2 gene. HER2 proteins are receptors on breast cells. They’re involved in normal cell growth. HER2 appears on some cancer cells, particularly for breast and ovarian cancers.

Sometimes, the HER2 protein doesn’t work correctly. This can cause the cells to multiply too quickly. Excessive reproduction can cause a fast-growing breast cancer.

If HER2 is present in your breast cancer cells, it’s known as HER2-positive breast cancer. HER2-positive breast cancer occurs in approximately 25 percent of breast cancer cases.

HER2 was discovered in the 1980s. At this time, researchers realized that the presence of the HER2 protein could cause cancer to spread more quickly to other parts of the body. This discovery led to research on how to slow or alter the growth process of these cancer cells. In the last 20 years, there have been significant treatment options developed to treat HER2-positive breast cancer.

If breast cancer cells don’t contain HER2, the condition is called HER2-negative breast cancer. If you have HER2-negative breast cancer, your doctor will consider breast cancer groups 1 and 4 when determining a treatment plan. Group 1, or luminal A, breast cancers are likely to benefit from hormone therapy and chemotherapy. Group 4, or basal-like, breast cancers are likely to benefit from chemotherapy.

There are several tests that can determine your HER2 status, including:

  • an immunohistochemistry (IHC) test
  • a fluorescence in situ hybridization (FISH) test
  • the Subtraction Probe Technology Chromogenic In Situ Hybridization (SPoT-Light HER2 CISH) test
  • the INFORM HER2 Dual In Situ Hybridization (INFORM HER2 Dual ISH) test

It’s important to know the HER2 test used because it will determine whether you’ll respond to certain medications for HER2-positive breast cancers. Generally, doctors use an IHC test first. FISH tests are thought to be more accurate, but they’re more expensive and the results can take longer.

For more than 30 years, researchers have been studying HER2 and ways to treat it. Successful targeted treatments have now changed the outlook of stage 1 to 3 breast cancers from poor to good.

The humanized monoclonal antibody trastuzumab, also known as Herceptin, has improved the outlook of those with HER2-positive breast cancer when used in tandem with chemotherapy. A 1998 showed that this combination of treatment slowed the growth of HER2-positive breast cancer when compared to treating it with just chemotherapy alone. For some, the use of trastuzumab with chemotherapy has resulted in long-lasting remissions.

Other treatments for HER2-positive breast cancer include lapatinib (Tykerb). This medication can be used in combination with capecitabine (Xeloda), a type of chemotherapy, or letrozole (Femara), a type of hormonal therapy.

In 2013, a new drug, ado-trastuzumab emtansine (Kadcyla), debuted. This medication shows the potential to be an effective initial treatment with fewer side effects than trastuzumab.

The Cleveland Clinic is currently conducting trials to determine the effectiveness of two powerful, targeted drugs. The aim of the study is “to develop an optimum long-term treatment protocol” with minimum side effects that also doesn’t require chemotherapy.

If you’ve been diagnosed with invasive breast cancer, make sure your doctor tests you for your HER2 status. The results of the test will determine the best options for treating your cancer.

New developments in the treatment of HER2-positive breast cancer have improved the outlook for people with this condition. Treatment may be able to slow the growth of HER2 proteins in cancer cells.