HER2low And What You Need To Know

HER2low And What You Need To Know

HER2 (human epidermal growth factor receptor 2) is a protein present in normal cells that helps to regulate cell growth and division. The HER2 gene makes this HER2 protein, which is located on the cell surface.  In about 1 in 5 breast cancers, the HER2 gene makes extra copies of itself, which means the cell makes too much of this protein.  This is called HER2 overexpression.  This leads the cancer cells to divide more quickly, which means that HER2 positive breast cancers can be more aggressive.  These cancers are often treated with Herceptin.

Individuals who have low or equivocal expression of HER2 usually don’t qualify to use Herceptin.  However, if the cancer recurs, and especially if it becomes metastatic, women are able to have new testing with can identify tumors that are “HER2low”.  These are tumors that have some expression of HER2, maybe 1+ or 2+, but not overexpression.  They can then be treated with an antibody-drug conjugate called trastuzumab deruxtecan, brand named “Enhertu”.  This medication connects the antibody that recognizes the HER2 protein on the cell surface with a strong drug to kill the cancer cells.  The antibody portion delivers the drug specifically to the HER2 positive cells, allowing to be very effective at targeting and killing cancer cells.

If your cancer was identified as HER2 negative at the time of diagnosis, there is a good chance the tumor can be retested to see if it is HER2low.  About 75% of those with recurrent or advanced breast cancer will either be HER2 positive, or HER2 low, and can consider using these medications.  You can ask your oncologist about this kind of testing and treatment.

This blog series was made possible with generous support from AstraZeneca. You can find more education within this series here.

Sharsheret is a national not for profit cancer support and education organization and does not provide any medical advice or perform any medical procedures. Sharsheret does not endorse or promote any specific medication, treatment, product, or service, and makes no guarantees regarding the effectiveness of the product discussed herein. The information provided herein is not a substitute for professional medical advice or treatment. You should always seek the advice of your physician or other qualified health provider.