What Is HER2-Positive Breast Cancer?

What is HER2-positive breast cancer?

HER2 (human epidermal growth factor receptor 2) is a transmembrane tyrosine kinase receptor and is expressed by, and involved in the growth of, some cancer cells. For example, HER2 is overexpressed in 18% to 20% of invasive breast cancers and affects treatment as well as prognosis of breast cancers.

• In about 10%-20% of breast cancers, the cancer cells test positive for HER2, sometimes referred to as the HER2/neu protein.
• HER2 is a growth-promoting protein located on the surface of some cancer cells.
• HER2-positive breast cancers tend to grow more rapidly and spread more aggressively than breast cancers that are HER2-negative.

What causes HER2-positive breast cancer?

Doctors do not know what specifically causes some breast cancers to express this protein while others do not.

All patients with invasive breast cancer should have their tumor cells tested for HER2. Medical professionals routinely perform this test in the pathology laboratory at the time of diagnosis, using the sample of your breast tissue removed for diagnosis. The testing for HER2 can involve one or more of the following tests.

Health care professionals may use either immunohistochemistry (IHC) to identify the HER2 protein or in-situ hybridization (ISH) testing to look for the gene.

1. IHC test: This test shows if there is too much HER2 protein in the cancer cells and is graded 0 to 3.
2. FISH test: This test evaluates if there are too many copies of the HER2 gene in the cancer cells. This test is either positive or negative.
3. SPoT-Light HER2 CISH test: This test also evaluates if there are too many copies of the HER2 gene in the cancer cells and is reported as positive or negative.
4. Inform HER2 Dual ISH test: This test also evaluates if there are too many copies of the HER2 gene in the cancer cells and is reported as positive or negative.

The signs and symptoms for HER2-positive breast cancers are the same as for HER2-negative breast cancers, except for the fact that HER2-positive cancers are likely to grow faster and are more likely to spread. The following are possible signs of breast cancer:

• Thickening or lump in the breast that feels different from the surrounding area
• Inverting of the nipple
• Nipple discharge or redness 
• Breast or nipple pain
• Swelling in your armpit or collarbone could mean breast cancer has spread to lymph nodes in that area
• Swelling of part of the breast
• Redness
• Changes in the skin of the breast
• Skin dimpling (peau d'orange)
• Lymph node changes

Your health care team needs to evaluate all therapy and provide guidance in response to all test results available and the specific circumstances of your cancer. Treatment for HER2-positive breast cancer typically involves a combination of chemotherapy and specific drugs used for cancers expressing the HER2 protein:

• Trastuzumab (Herceptin): This is a monoclonal antibody against HER2, as well as the first drug developed that targets the HER2 protein.
• Pertuzumab (Perjeta): This is another monoclonal antibody that targets HER2-positive cancers.
• Ado-trastuzumab emtansine or TDM-1 (Kadcyla): It's a monoclonal antibody that is attached to a chemotherapy drug, emtansine.
• Lapatinib (Tykerb): Medical professionals usually use this kinase inhibitor with chemotherapy or hormone therapy.
• Neratinib (Nerlynx) interferes with the cancer cells' ability to respond to growth signals.

As mentioned before, HER2-positive breast cancers are more likely to grow faster and to come back after treatment than cancers that are HER2-negative. However, the development of the drugs discussed above that specifically treat cancers expressing HER2 has led to significant improvements in the outlook for people with HER2-positive breast cancer. While survival rate statistics for breast cancer are not broken down to show rates for HER2-positive cancers, the 5-year survival rate for all localized breast cancers is 99%. However, the 5-year survival rate for metastatic breast cancer is 27%, so it is important to treat HER2-positive breast cancer as early as possible to reduce or prevent spread.