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What Is HER2-Positive Breast Cancer?

About 1 of every 5 of breast cancers are HER2-positive. That means the cancer cells have more of the protein HER2/neu. These cells grow and spread faster than the ones with normal levels of the protein.

Even though this form of cancer is more aggressive than other types, there are treatments that can help.

Your doctor will test your cancer to find out if it's HER2-positive. Then you’ll work together to come up with a treatment plan that's best for you.


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

Genes don’t play the same role in this type of cancer as with other kinds. You can't inherit a bad copy of this gene from a parent, and you won’t pass it on to your children.


The most common warning sign 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
  • Change in its shape
  • 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 showed the cancer. 

Getting a Diagnosis

When you're diagnosed with breast cancer, your doctor will check to see if you have HER2. He’ll probably give you one or more of these four tests.

The IHC test (immunohistochemistry) looks 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:

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

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