From Benjamin T. Herms, MD, medical oncologist and hematologist

January 6, 2023

The average woman has a one in eight chance of developing breast cancer. As a result of the recent FDA approval of a new breast cancer treatment, we now have another breast cancer classification subtype: HER2-low. What does this mean for treatment options and should breast cancer patients have their tumors re-tested?

As part of their breast cancer diagnosis, patients’ breast cancer tissue is sampled and tested in a lab for biomarkers including hormones and the HER2 protein that might be fueling tumor growth. In this era of precision medicine, these test results help doctors select the best treatment option for every patient’s individual cancer. Until recently, patients were told whether or not their cancer cells tested positive or negative for the HER2 protein. Now, we also have the HER2-low classification.

HER2 (human epidermal growth factor 2) is a protein found on the surface of most breast cancer cells and levels of the protein can be different from one patient to the next. Using immunohistochemistry (IHC) testing in a lab, pathologists evaluate breast tissue samples and assign them a score of 0-3+:

  • Patients scoring 3+ are HER2-positive.
  • Patients receiving a 2+ are considered borderline and receive additional testing to determine the positive or negative classification.
  • Patients scoring 0-1+ are HER2-negative.

According to the FDA, of the new cases of female breast cancer diagnosed in 2022, 80-to-85 percent were previously considered to be HER2-negative. The concept of HER2-low was introduced in the DESTINY-Breast04 clinical trial, and the results of the study were presented at the ASCO (American Society of Clinical Oncology) Annual Meeting this past summer. HER2-low was defined as having a score of 1-2 on IHC. The phase three trial evaluated Enhertu for patients with HER2-low breast cancer that had metastasized (spread) or was unable to be surgically removed.

As a result of the DESTINY-Breast04 clinical trial, about 60 percent of 2022 breast cancer cases are now considered HER2-low and eligible for the newly FDA-approved Enhertu, a precision targeted therapy. Enhertu is now another option for these patients if they develop resistance to standard treatment options of chemotherapy, endocrine therapy, or immunotherapy. Study results revealed that patients using Enhertu had prolonged survival.

Because HER2-low is an evolving concept, we anticipate that treatment approaches will also evolve. We recommend that newly diagnosed patients confirm their precise HER2 status with their doctors. If your tumor was previously tested, ask your doctor to retest it as the results could impact your treatment.

OHC has a team of fellowship-trained breast surgeons who collaborate with a multidisciplinary team of leading cancer experts that include medical, gynecologic, and radiation oncologists; hematologists, blood and marrow transplant specialists, cellular therapy specialists, radiology, pathology, and plastic surgery. To learn more about OHC’s breast surgical oncology team or to request a second opinion, call 1-888-649-4800 or visit

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