Human epidermal growth factor receptor 2 is a gene that makes proteins in the breast. It can play a role in the development of breast cancer.

These proteins act as receptors on breast cells and are important for maintaining a healthy cell lifecycle.

Normally, human epidermal growth factor receptor 2 (HER2) helps control how a healthy breast cell divides, grows, and repairs itself.

However, when the HER2 gene is abnormal, it causes the cells to divide and grow at an uncontrolled rate.

HER2-positive breast cancer is a more aggressive type of breast cancer compared with HER2-negative types. Excessive amounts of the gene and the protein receptors it produces encourage the rapid growth of cancer cells.

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With an early diagnosis and treatment, the outlook for breast cancer is good.

At the moment, doctors are not sure exactly what causes HER2 gene abnormalities.

Factors that may play a role in include:

  • the environment
  • genes
  • lifestyle

There may be genetic components.

However, experts believe that it is not possible to inherit a bad HER2 gene from a parent, so it is not hereditary.

HER2-positive breast cancer tends to grow faster, spread more easily, and be more likely to come back than HER2-negative breast cancer.

Symptoms of HER2-positive breast cancer are the same as for any other type of breast cancer.

The most typical sign is a lump in the breast that is harder than the surrounding area.

Other symptoms may include:

  • change in breast shape
  • breast swelling
  • discharge from the nipple that is not breast milk
  • pain in the breast or nipple
  • redness or thickness of the nipple or breast skin
  • skin irritation or dimpling

Detection of breast cancer can happen at home with a self-exam or at a doctor’s office with a mammogram.

If a doctor confirms an unusual growth, they will run tests to determine if the lump is breast cancer. From there, they will determine if the cancer is HER2-positive.

Four main tests can determine if HER2-positive cancer is present.

These tests include:

  • FISH (fluorescent in situ hybridization) test: A positive or negative test used to find out if there are high levels of the HER2 gene in breast cancer cells.
  • IHC (immunohistochemistry) test: This test determines if there is too much HER2 protein in breast cancer cells. A score of 0 or 1+ is negative, 2+ is borderline, and 3+ is positive.
  • Inform HER2 dual ISH test: This test shows if breast cancer cells are HER2-positive.
  • SPoT-Light HER2 CISH test: This identifies whether there are too many copies of the HER2 gene in breast cancer cells.

An incorrect test result can result in misdiagnosis.

People should ask their doctor how confident they are in the results and should ask for additional testing if a result comes back as borderline. They may wish to seek a second opinion.

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Kadcyla, a form of targeted chemotherapy, may be used in the treatment of HER2-positive breast cancer.

There are several treatment options available for HER2-positive breast cancer, depending on the type and stage.

The doctor will help determine which of these treatments is best.

As diagnostic methods become more precise, doctors are able to recommend more specific drugs for each case and type of HER2.

As a first-line treatment for HER2-positive breast cancer, a doctor will likely recommend a combination of the following targeted therapies:

  • trastuzumab (Herceptin)
  • pertuzumab (Perjeta)
  • a taxane, except if the person has a contraindication to taxanes

If the cancer continues to progress despite the treatment, the doctor will review the case and make new recommendations.

Other HER2-positive breast cancer treatments can include:

  • Trastuzumab emtansine (Kadcyla): A form of targeted chemotherapy.
  • Lapatinib (Tykerb): A chemical that targets HER2-positive breast cancer cells.
  • Neratinib (Nerlynx): A kinase inhibitor that blocks certain enzymes that promote cell growth.

The doctor may also recommend endocrine, or hormonal, treatments if the cancer is estrogen- or progesterone-positive.

Lifestyle choices

In addition to treatment, anyone with a diagnosis of HER2-positive breast cancer should live healthfully, as far as possible. A healthful lifestyle may also reduce the risk of developing breast cancer.

This includes:

  • Diet: There appears to be a link between obesity and diabetes and the incidence of breast cancer.
  • Exercise: Physical activity promotes general health and helps prevent a range of conditions.
  • Lifestyle: Smoking and excessive alcohol use increase the risk of developing various types of cancer and other conditions.

On receiving a diagnosis of HER2-positive breast cancer, it can also be helpful to:

  • seek support from friends and family
  • ask questions of their doctors and other healthcare providers

It is important to find out all you can about the options, discuss them with a doctor, and make sure the doctor knows your preferences. This will enable you to take an active role in your treatment.

HER2-positive cancer cells are present in roughly 25 percent of all breast cancer cases. Women with HER2-positive cells are more likely to be younger and have a more aggressive form of breast cancer.

Doctors describe breast cancer in stages from 0–4, depending on how far the disease has progressed.

According to the American Cancer Society, the 5-year life expectancy is as follows:

  • Stage 0: Close to 100 percent
  • Stage 1: Close to 100 percent
  • Stage 2: 93 percent
  • Stage 3: 72 percent
  • Stage 4 (the metastatic stage): 22 percent

The earlier a person receives a diagnosis and treatment for breast cancer, the better chances of survival they have.

The length of time a person with breast cancer will survive depends on:

  • the individual
  • how advanced the cancer is
  • when it is discovered
  • how it is treated

HER2-positive tends to be a more aggressive cancer compared with hormone-positive cancers and triple negative cancers.

HER2-positive cancers can also be hormone-positive cancers, such as estrogen receptor-positive (ER-positive), progesterone receptor-positive (PR-positive), or both.

In these cases, treatment may also include hormone therapy.

With an early diagnosis and appropriate treatment, early, the overall outlook for HER2-positive breast cancer is good.