Human epidermal growth factor receptor 2 (HER2) makes proteins in the breast. These proteins act as receptors on breast cells and are important in maintaining a healthy cell lifecycle.
In most cases, HER2 receptors help 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.
At the moment, doctors are not sure exactly what causes HER2 gene abnormalities. Some ideas on its origin include environment, genes, and lifestyle. However, experts believe that it is not possible to inherit a bad HER2 gene from a parent, so it is not hereditary.
Role of HER2 in breast cancer
HER2-positive breast cancer is aggressive and fosters the relatively fast growth, and spread, of cancer cells.
HER2-positive breast cancer is a more aggressive type of breast cancer compared to HER2-negative types.
Excessive amounts of the gene, and the protein receptors it produces, encourage the rapid growth of cancer cells.
HER2-positive breast cancer tends to grow faster, spread more easily, and is more likely to come back than HER2-negative breast cancer.
Tests for HER2
There are four main tests that doctors use to determine if a woman has HER2-positive cancer. These tests include the:
- FISH test: A positive or negative test used to discover if there is an excess of the HER2 gene in the breast cancer cells.
- IHC test: This test determines if there's too much HER2 protein in the 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 the breast cancer cells are HER2-positive.
- SPoT-Light HER2 CISH test: This identifies whether there are too many copies of the HER2 gene in the breast cancer cells.
A failed test can result in misdiagnosis, which could mean a HER2-positive breast cancer is not detected.
People should ask their doctor how confident they are in the results and should ask for follow up testing if a result comes back as borderline. Also, if needed, a person should seek out a second opinion.
Diagnosis and early detection
Symptoms of HER2-positive breast cancer are the same as for any other type of breast cancer. The most typical sign is a lump on the breast that is harder than the surrounding area.
The most common indication of HER2-positive breast cancer is a lump in the breast, much like other types of breast cancer.
Other symptoms may include:
- change in breast shape
- breast swelling
- discharge from the nipple
- 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.
Once diagnosed, the doctor will run tests to determine if the lump is breast cancer, and from there, will determine if the cancer is HER2-positive.
Unlike some other breast cancers, the HER2-positive breast cancer cells do not respond well to hormone treatment.
However, there are several other treatment options available. The doctor will help determine which of these treatments is best.
HER2-positive breast cancer treatments can include:
- Kadcyla: A form of targeted chemotherapy.
- Tykerb: A chemical that targets HER2-positive breast cancer cells.
- Perjeta: Blocks the HER2-positive cancer cells ability to receive signals to grow.
- Herceptin: Also blocks growth signals to HER-2 positive cancer cells.
In addition to treatment, people diagnosed with HER2-positive breast cancer should make sure they look after their overall health and well-being.
People diagnosed with HER2-positive breast cancer should seek out support from friends and family, ask questions of their doctors, exercise as life permits, and stay nourished.
Most of all, it is important for them to remember they are able to take an active role in how they are treated for HER2-positive breast cancer.
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 in age and have a more aggressive form of breast cancer.
Hormone positive cancers, such as estrogen receptor-positive (ER-positive) or progesterone receptor-positive (PR-positive) breast cancer may also be present for people with HER2-positive breast cancer. In those cases, treatment would need to target both of the problem areas.
People with HER2-positive breast cancer are likely to be younger. When it is caught and treated early, there tends to be a positive long-term outlook.
The length of time a person with breast cancer will survive depends on the individual, how advanced the cancer is, when it is discovered, and how it is treated.
HER2-positive tends to be a more aggressive cancer compared to hormone positive cancers and triple negative cancers.
In general, breast cancer survival rates are broken down across five stages from 0 to 4. 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 the breast cancer is discovered and treated, the better chances of survival the person has. When HER2-positive breast cancer is caught and treated early, people can have an overall good outlook.