HER2-Positive Breast Cancer: Causes, Symptoms, and Treatment
Medically reviewed by Achuta Uppu, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats HER2-Positive Breast Cancer?
An oncologist (a cancer doctor) usually leads care for HER2-positive breast cancer. A breast surgeon (a doctor who operates on the breast) often joins the care team. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is HER2-Positive Breast Cancer?
HER2 is a protein that helps breast cancer cells grow quickly. Breast cancers with higher levels of HER2 are called HER2-positive.
These cancers tend to grow and spread faster than HER2-negative breast cancers. But they are much more likely to respond to drugs that target the HER2 protein.
Symptoms
These are symptoms of breast cancer in general. They include:
- A new lump or thickening in or near the breast or in the armpit.
- A change in the size or shape of the breast.
- A dimple or puckering in the skin of the breast. It may look like the skin of an orange.
- A nipple turned inward into the breast.
- Nipple discharge other than breast milk.
- Scaly, red, or swollen skin in the nipple area or the breast.
- Pain in any area of the breast.
Causes and who gets it
In about 15% to 20% of breast cancers, the cancer cells make too much HER2. The sources used here do not name a cause for this.
Some cancers have other features too. A triple-positive cancer is HER2-positive, ER-positive, and PR-positive. That means it also has estrogen and progesterone receptors.
How doctors diagnose it
All invasive breast cancers should be tested for HER2. The test is done on the biopsy sample or on the tumor after surgery.
Doctors use one of two tests, called IHC and FISH. IHC uses lab-made antibodies that stick only to HER2. A color change shows up under a microscope. IHC results are 0, 1+, 2+, or 3+. FISH counts the copies of the HER2 gene in each cell.
A cancer is HER2-positive if the IHC result is 3+. It is also HER2-positive if IHC is 2+ and FISH is positive. Your cancer care team will use the result to choose treatment.
Treatment
Treatment for breast cancer can include surgery, radiation therapy, chemotherapy, hormone therapy, and targeted therapy. HER2-positive cancers are usually treated with drugs that target HER2. These are a kind of targeted therapy, which means medicine aimed at certain proteins on cancer cells. Several types are used:
- Monoclonal antibodies, such as trastuzumab and pertuzumab. They attach to HER2 on cancer cells and can help stop the cells from growing. Trastuzumab is often given with chemotherapy. For early breast cancer it is usually given for a year.
- Antibody-drug conjugates. Each one joins a HER2 antibody to a chemotherapy drug. The antibody acts like a guided delivery system that takes the chemotherapy into the cancer cell.
- Kinase inhibitors, such as lapatinib, neratinib, and tucatinib. These are pills.
They may be given before or after surgery. Triple-positive cancers are treated with hormone therapy as well as drugs that target HER2.
The side effects are often mild, but some can be serious. Heart damage is possible with monoclonal antibodies and antibody-drug conjugates. Your team will check your heart before treatment and during it. Diarrhea, hand-foot syndrome (sore, red hands and feet that may blister or peel), and liver problems can also happen with some of these drugs. Serious lung disease has been reported with fam-trastuzumab deruxtecan (Enhertu). These drugs can harm an unborn baby, so do not take them if you are pregnant.
When to see a doctor
See a doctor about any new breast lump or other breast change so the cause can be found. If you are in treatment, tell your cancer care team right away if you have a fast heartbeat, leg swelling, or severe tiredness. Also tell them about yellow skin or eyes, dark urine, or pain in the upper right belly.
Call 911 or go to the emergency room if you have chest pain, fainting, or severe trouble breathing.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Such a doctor can help with a breast change that needs a first look. They can arrange tests, help you understand the results, and coordinate your cancer team. They can also help with general health and follow-up during and after cancer care.
Common questions
What does HER2-positive mean?
HER2-positive means the cancer cells have too much of a protein called HER2. This protein helps breast cancer cells grow quickly. A cancer is HER2-positive if the IHC test is 3+, or if IHC is 2+ and the FISH test is positive.
Is HER2-positive breast cancer more aggressive?
Yes, it tends to grow and spread faster than HER2-negative breast cancer. But it is also much more likely to respond to drugs that target the HER2 protein.
How is HER2 status tested?
HER2 status is tested with an IHC test or a FISH test on the tumor sample. IHC uses lab-made antibodies that show HER2 under a microscope. FISH checks whether there are more copies of the HER2 gene per cell than normal.
Do HER2 drugs have side effects?
Yes. The side effects are often mild, but some can be serious. Heart damage is possible, so the care team checks your heart function before and during treatment. Tell your team about a fast heartbeat or leg swelling.
Sources
- American Cancer Society - Breast Cancer HER2 Status
- American Cancer Society - Targeted Therapy for Breast Cancer
- MedlinePlus - Breast Cancer
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
