--- title: "HER2-Positive Breast Cancer: Testing, Treatment & Outlook" description: "HER2-positive breast cancer grows faster, but targeted drugs including trastuzumab have transformed outcomes. Early-stage survival is high." url: https://breastcancer-charity.org/about-breast-cancer/her2-positive-breast-cancer/ robots: noindex --- # HER2-Positive Breast Cancer: Testing, Treatment & Outlook Breast health information HER2-positive breast cancer grows faster, but targeted drugs including trastuzumab have transformed outcomes. Early-stage survival is high. Treatment and care explained. ## Quick answer HER2-positive breast cancer is defined by excess HER2 protein that drives cancer cell growth. Targeted therapies including trastuzumab (Herceptin) and pertuzumab have dramatically improved survival — five-year survival for early-stage HER2-positive breast cancer now exceeds 90%. **Your next step:** see a GP (or your doctor, if you live outside the UK) about any new breast or chest change. These guides explain general information; your care team can advise on your own situation. **Content updated:** 28 May 2026 . Independent clinical review has not yet been recorded for this page. [How we prepare health information](https://breastcancer-charity.org/editorial-policy/) · [Report an error](https://breastcancer-charity.org/corrections/) At a glance HER2-positive breast cancer accounts for around 15–20% of all breast cancers Five-year survival for early-stage HER2-positive disease now exceeds 90% with targeted therapy Dual HER2 blockade (trastuzumab + pertuzumab) is standard for high-risk early and metastatic disease HER2-low (IHC 1+ or 2+) accounts for ~55–60% of all breast cancers and can be targeted with Enhertu ## What does HER2-positive mean? HER2 (human epidermal growth factor receptor 2) is a protein that promotes the growth of cells. In around 15–20% of breast cancers, cancer cells produce too much HER2 protein — a process called HER2 overexpression, caused by amplification (extra copies) of the HER2 gene. HER2-positive tumours tend to grow faster and spread more readily than HER2-negative tumours. Before targeted therapies existed, HER2-positive breast cancer carried a worse prognosis. Today, with modern targeted treatments, it is one of the most treatable forms of breast cancer. ## How is HER2 status tested? HER2 status is determined from a biopsy sample. Two laboratory tests are used: immunohistochemistry (IHC), which measures the amount of HER2 protein on the surface of cancer cells (scored 0, 1+, 2+ or 3+), and fluorescence in situ hybridisation (FISH), which measures the number of HER2 gene copies. Results are classified as HER2-positive (IHC 3+, or IHC 2+ confirmed by FISH amplification), HER2-low (IHC 1+ or IHC 2+ without gene amplification), or HER2-negative (IHC 0). ## Targeted treatments for HER2-positive breast cancer HER2-positive breast cancer is treated with drugs that specifically target cells expressing the HER2 protein, leaving most healthy cells unaffected. The main targeted therapies are: - Trastuzumab (Herceptin): The original HER2-targeted therapy. Given by intravenous infusion alongside chemotherapy for early and advanced HER2-positive breast cancer. Standard treatment for over 25 years. - Pertuzumab (Perjeta): Often combined with trastuzumab for high-risk early breast cancer and metastatic disease. The combination (dual HER2 blockade) is now the standard of care. - Ado-trastuzumab emtansine (T-DM1 / Kadcyla): An antibody-drug conjugate. Used for early HER2-positive breast cancer with residual disease after neoadjuvant treatment. - Trastuzumab deruxtecan (T-DXd / Enhertu): A newer antibody-drug conjugate approved for HER2-positive and HER2-low [metastatic breast cancer](https://breastcancer-charity.org/about-breast-cancer/secondary-breast-cancer/). Has significantly improved survival in advanced disease. - Tucatinib (Tukysa) and lapatinib: Oral tyrosine kinase inhibitors. Particularly useful when breast cancer has spread to the brain. - Neratinib (Nerlynx): An oral extended adjuvant therapy for early-stage ER-positive/HER2-positive breast cancer taken after one year of trastuzumab. ## Prognosis and survival Before targeted therapies, HER2-positive breast cancer had a significantly worse prognosis than HER2-negative disease. Modern treatments have transformed this. For early-stage HER2-positive breast cancer, five-year survival now exceeds 90% when treated with surgery, chemotherapy and targeted therapy. For metastatic HER2-positive disease, median overall survival has improved from under 18 months in the late 1990s to over 4–5 years with modern regimens — and continues to improve with new drugs. ## HER2-positive and hormone receptor-positive breast cancer Around 50% of HER2-positive breast cancers are also hormone receptor-positive (ER+ or PR+). These tumours are driven by both HER2 overexpression and oestrogen. Treatment combines targeted HER2 therapy, chemotherapy and endocrine therapy ([tamoxifen](https://breastcancer-charity.org/about-breast-cancer/hormone-therapy-side-effects/) or an aromatase inhibitor), typically continued for 5–10 years after completing chemotherapy and targeted therapy. ## What is HER2-low breast cancer? HER2-low is a newly recognised category (clinically relevant since 2022) for breast cancers that express a small amount of HER2 — more than zero (IHC 1+ or 2+/FISH-negative), but not enough to be classified as HER2-positive (IHC 3+). It accounts for approximately 55–60% of all breast cancers. The distinction has become clinically important because trastuzumab deruxtecan (Enhertu) specifically targets HER2-low tumours and has significantly improved outcomes in metastatic HER2-low disease, opening a new treatment pathway for a large group of patients. ## Frequently asked questions What is HER2-positive breast cancer? HER2-positive breast cancer has excess amounts of HER2 (human epidermal growth factor receptor 2) protein on cancer cells, which drives faster growth. Around 15–20% of breast cancers are HER2-positive. These tumours tend to grow more quickly than HER2-negative cancers. However, targeted therapies including trastuzumab (Herceptin), pertuzumab and newer antibody-drug conjugates have dramatically improved outcomes — five-year survival for early-stage HER2-positive cancer now exceeds 90%. Is HER2-positive breast cancer aggressive? HER2-positive breast cancer tends to grow and spread more quickly than HER2-negative cancer. Before targeted therapies became available, it carried a worse prognosis. Today, with modern treatments, outcomes for HER2-positive breast cancer are very good. Five-year survival for early-stage disease exceeds 90%, and even for metastatic disease, median survival has improved dramatically from under 18 months to over 4–5 years with the latest regimens. What is the treatment for HER2-positive breast cancer? Treatment for HER2-positive breast cancer typically combines surgery, chemotherapy and targeted HER2 therapy. The standard targeted drugs are trastuzumab (Herceptin) and pertuzumab (Perjeta), often given together. For early-stage disease with residual cancer after initial treatment, T-DM1 (Kadcyla) is used. For metastatic disease, trastuzumab deruxtecan (Enhertu) has significantly improved survival. Oral drugs including tucatinib and neratinib are also used in specific situations. What does HER2-low mean? HER2-low describes breast cancers that express a small amount of HER2 protein — not enough to qualify as HER2-positive (IHC 3+), but detectable (IHC 1+ or IHC 2+/FISH-negative). It accounts for approximately 55–60% of all breast cancers. This category has become clinically important since 2022 because trastuzumab deruxtecan (Enhertu) has shown striking efficacy in HER2-low metastatic breast cancer, offering a new targeted treatment pathway for a large population of patients. Is HER2-positive breast cancer hereditary? HER2-positive breast cancer is generally not hereditary. HER2 positivity results from acquired gene amplification (extra copies of the HER2 gene that develop in cancer cells during a person's lifetime), not from inherited mutations. However, inherited mutations such as BRCA1 and BRCA2 can lead to breast cancers that happen to also be HER2-positive. If you have a strong family history, your oncologist can arrange genetic testing to check for inherited mutations. ## Sources and further reading - [NHS inform: breast cancer in women](https://www.nhsinform.scot/illnesses-and-conditions/cancer/cancer-types-in-adults/breast-cancer-in-women/) - [NICE NG101: HER2-positive breast cancer](https://www.nice.org.uk/guidance/ng101/chapter/Recommendations#her2-positive-breast-cancer) - [NICE TA569: pertuzumab for HER2-positive early breast cancer](https://www.nice.org.uk/guidance/ta569) - [NICE TA632: trastuzumab emtansine for HER2-positive early breast cancer](https://www.nice.org.uk/guidance/ta632) - [NICE TA612: neratinib for HER2-positive early breast cancer](https://www.nice.org.uk/guidance/ta612) - [NICE TA509: pertuzumab with trastuzumab and docetaxel](https://www.nice.org.uk/guidance/ta509) - [NICE TA862: trastuzumab deruxtecan for HER2-positive advanced breast cancer](https://www.nice.org.uk/guidance/ta862) - [NICE TA992: trastuzumab deruxtecan for HER2-low breast cancer](https://www.nice.org.uk/guidance/ta992) This content is for educational purposes and does not constitute medical advice. Always consult a qualified healthcare professional for personal medical guidance. Source links do not imply endorsement by the NHS or another organisation. See our [editorial policy](https://breastcancer-charity.org/editorial-policy/). ## Keep reading [Support ### Where can I get breast cancer support in the UK?](https://breastcancer-charity.org/breast-cancer-support/) [🔬 ### What are the different types of breast cancer?](https://breastcancer-charity.org/about-breast-cancer/types-of-breast-cancer/)[💊 ### What treatments are used for breast cancer?](https://breastcancer-charity.org/about-breast-cancer/breast-cancer-treatment/)[⚡ ### What is triple-negative breast cancer?](https://breastcancer-charity.org/about-breast-cancer/triple-negative-breast-cancer/)