HER2 positive breast cancer

What HER2 positive breast cancer is

About one breast cancer in six makes far too much of a growth protein called HER2. Twenty years ago that made it one of the harder types to treat. Medicines that block HER2, starting with trastuzumab, changed that, and today HER2 positive cancer responds to treatment as well as any type. A report is HER2 positive when the staining score is 3+, or when it is 2+ and a second test called FISH confirms extra copies of the gene. HER2 positive cancer can also be hormone receptor positive, in which case it is sometimes called triple positive and gets both kinds of medicine.

What usually happens next with HER2 positive breast cancer, in order

1. Medicine first, for most. When the cancer is larger than about 2 cm or has reached a lymph node, treatment before surgery is standard: a few months of chemotherapy together with two HER2-blocking antibodies, trastuzumab and pertuzumab. Before it starts, a clip is placed in the tumor and in any abnormal node so the surgeon can find them afterward, and the heart is checked with an ultrasound because HER2 medicines can affect it.
2. Surgery. Often smaller than it would have been, because the cancer has shrunk. In a large share of people no cancer at all is found in the tissue removed, called a pathologic complete response. Whether cancer remains decides the next step.
3. Finishing the year. HER2-targeted treatment continues after surgery to complete about a year in total. If cancer remained at surgery, the medicine is usually switched to an antibody drug conjugate, which carries chemotherapy directly to HER2 cells.
4. Radiation, on the same rules as other types.
5. Endocrine therapy, if the cancer is also hormone receptor positive.

For small HER2 positive cancers, about 2 cm or less with clear nodes, surgery may come first, followed by a gentler chemotherapy with trastuzumab.

Choices you will be asked about with HER2 positive breast cancer

Whether to start with medicine or surgery, when the cancer is near the size threshold. Lumpectomy or mastectomy, decided after the medicine has done its work. Fertility preservation before chemotherapy, if you may want children. Port placement for the infusions.

Questions to bring to your appointment

These are built for HER2 positive breast cancer. The report decoder narrows the list further from your own report, and the print button there puts it on paper with room to write. Bring someone with you if you can; two sets of ears hear more than one.

• What is the exact type, grade, and receptor status, and can I have a copy of the report?
• What stage is it now, and what could change that after surgery?
• Should surgery come first, or medicine first, and why?
• Am I a candidate for a lumpectomy? If I chose mastectomy instead, would the outcome differ?
• How will the lymph nodes be checked, and what happens if one is positive?
• Which anti-estrogen medicine, for how long, and what side effects should I expect?
• Which HER2-targeted medicines, for how long, and how will my heart be monitored?
• Do I qualify for genetic testing, and should it be done before I decide on surgery?
• Do I need any scans of the rest of my body, and if not, why not?
• If I want to talk to a plastic surgeon before deciding, can that happen first?
• Is there a clinical trial I should know about?
• How much time do I have to decide? Is there anything that must be decided today?
• Who is my contact between appointments, and how do I reach them?
• Is there a nurse navigator or counselor I can be connected with?

Where this comes from

Published 7 September 2026 as part of the guide; a page of its own since 9 September 2026.