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What Is HER2-Positive Breast Cancer?

Hearing a diagnosis of breast cancer is scary. New research and treatments have meant more women are breast cancer survivors, though. 

If your breast cancer is HER2-positive, that means it has a certain protein (HER2) that makes cancer cells grow. It tends to be much more aggressive and fast-growing than other kinds of breast cancer, but there are effective treatments that target HER2.

About 20% to 25% of breast cancers are HER2-positive. Your doctor will test your cancer to find out if yours is, so you can make the right decisions about your treatment. Your doctor will also find out other things about your cancer that will help you treat it better, including whether it has spread and whether it's sensitive to hormones.

Learn all you can about your treatment options -- and get the emotional support you need -- to make things easier.


Researchers aren't sure what causes breast cancer. They think it may be a combination of things, including your genes and your environment.

In HER2-positive breast cancer, a gene causes cancer cells to make too much HER2 protein. When that happens, cancer cells grow in an out-of-control way.

This only happens in cancer cells. It can happen in other cancers, too -- not just breast cancer.

You can't inherit a faulty copy of this gene from a parent, or pass it on to your children.


The most common symptom of any type of breast cancer is a lump in your breast that feels different from the area around it.

Other symptoms include:

  • Breast swelling or a change in the shape of the breast
  • Skin irritation or dimpling
  • Pain in the breast or nipple
  • Redness or thickness of the nipple or breast skin
  • Discharge from the nipple (not breast milk)

You may have noticed a difference in your breasts during a self-exam, or you may have had a mammogram that found the cancer. 

Getting a Diagnosis

If you're diagnosed with breast cancer, your doctor will test for HER2. There are four types of tests for HER2-positive breast cancer:

The IHC test (immunohistochemistry) checks for how much HER2 protein is in a sample of breast cancer tissue.

Three other tests check to see if there are too many HER2 genes in the cancer cells:

  1. FISH test (fluorescence in-situ hybridization)
  2. SPOT-Light HER2 CISH test (subtraction probe technology chromogenic in-situ hybridization)
  3. Inform HER2 Dual ISH test (inform dual in-situ hybridization)

Sometimes the results of one test aren't clear, and your doctor may order another type of test.

Questions for Your Doctor

  • How are you sure my cancer is HER2 positive?
  • Where exactly is my cancer?
  • What stage is it?
  • What are my treatment options, and what do you recommend?
  • Should I have targeted treatment?
  • How quickly do I need to start treatment?
  • How will treatment make me feel?
  • Will I be able to work?
  • Do I need to have my breast removed?
  • Is my treatment covered by insurance?
  • What if my cancer doesn’t respond to treatment?