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HER2 Testing and What the Results Mean

HER2 status is one of several factors, including (https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/breast-cancer-her2-status.html) hormone receptor (HR) status, tumor size, and evidence of metastasis, clinicians use to understand disease prognosis and determine a treatment approach. Patients’ HER2 status is measured by two methods: immunohistochemistry (IHC) and in situ hybridization (ISH). IHC testing measures (https://www.cancer.org/cancer/breast-cancer/understanding-a-breast-cancer-diagnosis/breast-cancer-her2-status.html) the amount of HER2 protein, with results reported as 0, 1+, 2+ or 3+.

• Results of 0 or 1+ are considered HER2-negative, meaning that patients have a normal level of HER2 expression. Historically, HER2-targeted therapies have not been effective for these patients.
• A finding of 2+ is equivocal and typically will be confirmed by an ISH test, which counts the copies of the HER2 gene in cells. ISH results are either (https://pubmed.ncbi.nlm.nih.gov/29846122/) positive or negative for HER2 gene amplification.
• A result of 3+ is considered HER2-positive, meaning that patients have higher-than-normal levels of the HER2 protein and may be candidates for therapies that target HER2.

Implications for Treatment and Beyond

Breast cancer is typically treated with various combinations of surgery, radiation, chemotherapy, hormone therapy, or targeted therapy. Targeted therapies may be used for specific breast cancer types: HR-positive breast cancers are typically treated (https://doi.org/10.5858/arpa.2012-0617-OA) with endocrine therapies, whereas treatments that target HER2 may be used (https://doi.org/10.18632/oncotarget.7043) for HER2-positive breast cancers.

Targeted agents have unique side effects that oncology nurses must monitor and manage. For example, monoclonal antibodies that target HER2 could affect (https://voice.ons.org/news-and-views/breast-cancer-prevention-screening-diagnosis-treatment-side-effect-and-survivorship) cardiac function, so patients require regular ejection fraction evaluation. If adverse events progress beyond grade 1, doses may need to be adjusted, held, or discontinued, depending on the toxicity’s severity.

The development of targeted therapies has significantly improved survival for patients with HER2-positive breast cancer. Some of the nursing considerations for breast cancer survivorship care include (https://voice.ons.org/news-and-views/nursing-considerations-for-breast-cancer-survivorship-care):

• Monitoring and managing late and long-term effects
• Educating patients about ongoing screening and prevention strategies
• Developing and coordinating a survivorship care plan

However, HER2-positive metastatic breast cancer remains (https://doi.org/10.18632/oncotarget.7043) an incurable disease. Once patients progress on currently available anti-HER2 regimens, they have few treatment options. Most available therapies for patients with advanced disease have shown limited overall response rates and median progression-free survival benefits of less than six months beyond the second-line setting. Recent advancements in later-line therapy, including monotherapy and combination treatments, that target HER2-expressing metastatic breast cancer may offer meaningful clinical benefit.

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