HER2 Positive Breast Cancer

HER2-positive breast cancer was once considered one of the most aggressive forms of the disease, but thanks to major advances in targeted treatments, it has become one of the most successfully treated types of breast cancer.

Table of contents

• What is HER2 positive breast cancer?
• How common is this type of breast cancer?
• What causes HER2 positive breast cancer?
• Symptoms of HER2 positive breast cancer
• Risk factors
• Possible complications
• How is HER2 positive breast cancer diagnosed?
• Treatment options
• Outlook and prognosis
• Living well after treatment

What is HER2 positive breast cancer?

HER2-positive breast cancer is a type of invasive breast cancer (cancer that grows beyond where it started) that tests positive for a specific protein called human epidermal growth factor receptor 2, or HER2. This protein is found on the surface of all breast cells and normally helps manage cell growth and repair, making sure cells divide as needed to replace damaged or dying cells^[2][4].

In HER2-positive breast cancer, the cancer cells have extra copies of the gene that makes the HER2 protein. In about 1 of every 5 breast cancers, the cancer cells make too many copies of this gene. When there are too many HER2 genes, they produce too many HER2 proteins on the cell surface. These extra proteins act like receivers that pick up too many growth signals, causing breast cells to grow and divide much faster than normal, in an uncontrolled way^[1][2].

This type of breast cancer is fast-growing and more likely to spread from the breast to other areas of the body compared to some other types of breast cancer. However, it responds very well to treatments that specifically target the HER2 protein^[2].

How common is this type of breast cancer?

Between 15% and 20% of all breast cancer cases are HER2-positive. This means that if about 290,000 women are diagnosed with invasive breast cancer in a given year, roughly 43,500 to 58,000 of those cases would be HER2-positive^[2][3][5].

Men can also develop breast cancer, but HER2-positive breast cancer rarely occurs in men^[2].

What causes HER2 positive breast cancer?

HER2-positive breast cancer happens when the HER2 gene changes or mutates. Normally, the HER2 gene produces HER2 proteins that control how breast cells grow, divide, and repair themselves. When the gene mutates, it starts making more copies of itself. More HER2 genes lead to more HER2 proteins being made. With too many HER2 proteins on the cell surface, breast cells receive too many signals to grow and divide. This causes cells to multiply out of control and form cancerous tumors^[2][4].

Scientists discovered HER2-positive breast cancer in the 1980s while searching for genes that cause cancer. Researchers identified a link between the HER2 gene and cancer formation, showing that a mutation in this gene could cause normal cells to grow uncontrollably like cancer cells^[7].

Symptoms of HER2 positive breast cancer

Like many types of breast cancer, HER2-positive breast cancer may not cause obvious symptoms in its early stages. When symptoms do appear, they are similar to those of other breast cancers^[2]:

• A change in the size, shape, or outline of your breast
• A lump or mass in the breast, which may feel as small as a pea
• A lump or thickening in or near your breast or in your armpit that continues through your menstrual cycle
• Changes in how the skin on your breast or nipple looks or feels – the skin may look dimpled, puckered, scaly, inflamed, reddish, or darker than usual
• A marble-like hardened area under your skin
• A blood-stained or clear fluid coming from your nipple

Risk factors

The risk factors for HER2-positive breast cancer are the same as those for breast cancer in general. Many things may increase your risk, though you may develop breast cancer even without any of these risk factors^[2]:

• Having an inherited genetic mutation such as BRCA1 or BRCA2 (genes that, when changed, can increase cancer risk)
• Having a personal history of breast cancer
• Having certain breast conditions like atypical ductal hyperplasia (abnormal cell growth in breast ducts)
• Starting your menstrual cycle earlier than usual
• Starting menopause later than usual
• Taking hormone replacement therapy
• Having more than one alcoholic drink per day
• History of radiation therapy for conditions including some types of lymphoma

Possible complications

HER2-positive breast cancer can spread, or metastasize, to other parts of the body. About half of people with this type of breast cancer are diagnosed after the cancer has already spread to other areas of their body, including their brain. When breast cancer spreads to the brain, it can be life-threatening^[2].

Up to 50% of people with metastatic HER2-positive breast cancer can develop brain metastasis. However, newer treatments are becoming available that can better reach cancer cells in the brain^[5].

How is HER2 positive breast cancer diagnosed?

Healthcare providers diagnose all breast cancers through a breast biopsy, which involves removing a small sample of breast tissue for testing. If the biopsy finds cancer, a medical specialist called a pathologist examines the breast tissue cells under a microscope to look for signs of HER2 proteins^[2][3].

Experts recommend that every invasive breast cancer be tested for the presence of HER2 because the results significantly affect treatment decisions. Testing is not routinely done for ductal carcinoma in situ (DCIS, a very early form of breast cancer) except as part of a clinical trial^[1].

A biopsy is also used to check for other important markers, including estrogen receptor (ER) and progesterone receptor (PR). These results help doctors understand the tumor’s characteristics and determine the best treatment plan^[3][5].

HER2-positive cancers can be:

• HER2-positive and hormone receptor positive (ER-positive or PR-positive), sometimes called triple positive
• HER2-positive and hormone receptor negative (ER-negative and PR-negative)

The combination of these markers affects whether your treatment might involve both HER2-targeted therapy and hormone therapy, or just HER2-targeted therapy alone^[5].

If breast cancer comes back or spreads, the cancer cells should be tested again for HER2 and hormone receptor status, as these can change from the original diagnosis^[1].

Treatment options

HER2-positive breast cancer tends to be more aggressive than other types of breast cancer, but treatments that specifically target HER2 are very effective. These targeted treatments are so effective that the outlook for HER2-positive breast cancer is actually quite good^[1][5].

HER2-targeted therapies (also called anti-HER2 therapies or HER2 inhibitors) are medicines that attach to the HER2 protein receptors on the surface of breast cancer cells. By blocking these receptors, the medicines prevent them from receiving growth signals. This can slow or stop the growth of HER2-positive breast cancer^[15].

Some HER2-targeted medicines are monoclonal antibodies, which are made in a laboratory to work like the antibodies your immune system naturally makes. In addition to targeting HER2 receptors, these medicines can help your immune system recognize and destroy cancer cells^[15].

Some HER2 inhibitors are antibody-drug conjugates, which combine HER2-targeted therapy with chemotherapy medicine. These special medicines carry chemotherapy directly to the HER2-positive cancer cells, which helps protect healthy cells from the toxic effects of chemotherapy^[15].

For people with HER2-positive early breast cancer, chemotherapy combined with a HER2-targeted therapy called trastuzumab reduces the risk of the cancer coming back by half compared to chemotherapy alone. Trastuzumab is usually given for one year and may begin before breast cancer surgery or after surgery^[11].

Standard chemotherapy drugs can also be effective in treating HER2-positive breast cancers, although these drugs don’t specifically target the HER2 protein^[1].

Your doctor will decide which treatment is right for you based on several factors^[5]:

• The stage and size of the cancer
• Whether the cancer is HER2-positive or HER2-low
• Any earlier treatments you have had
• If the cancer grew after previous treatment
• The side effects associated with each treatment
• Whether your health insurance favors one medication over another

Women who are pregnant, plan to become pregnant, or are breastfeeding should not receive targeted therapies, as the limited research available suggests these treatments are not safe during pregnancy^[15].

Outlook and prognosis

Healthcare providers can successfully cure HER2-positive breast cancer if it is diagnosed before it spreads to other parts of the body. What used to be a diagnosis doctors dreaded giving has transformed into one where people with HER2-positive disease actually tend to do better than people with some other types of breast cancer, thanks to new therapies^[2][5].

When HER2-positive cancer is metastatic (stage 4), meaning it has spread beyond the breast and nearby lymph nodes to other parts of the body, treatment continues lifelong. The goal is to shrink or slow down tumor growth while maintaining quality of life for as long as possible^[5].

Living well after treatment

Taking care of your health and well-being becomes even more important when you’re dealing with HER2-positive breast cancer. Good self-care habits can help with stress, sleep problems, and anxiety, while also supporting your general health^[18].

Maintain a healthy weight. Studies show that gaining more than 10 percent of your body weight during or after breast cancer treatment increases the risk of cancer coming back and decreases overall survival time. Maintaining a healthy weight can improve overall health and reduce the risk of other diseases^[23].

Eat a well-balanced diet. A healthy diet has been shown to increase breast cancer survival. Research shows that a diet high in vegetables and fiber and low in fruit juices is linked to longer survival. Eating daily servings of vegetables like broccoli and cauliflower, as well as leafy greens, was associated with lower mortality risk. Eating large amounts of carbohydrates and saturated fat (found in red meat and high-fat dairy products) has been linked to worse outcomes^[23].

Stay physically active. Exercise is beneficial during and after treatment. Women who stay active during chemotherapy often seem to handle treatment better. Physical activity can help with some side effects that may come with cancer treatment, including effects on your heart and weight gain^[18].

Find support. Don’t be afraid to ask family and friends for help. Many people also find support groups helpful as a way to connect with others in a similar situation. If you need help managing your feelings, you may want to see a mental health professional who specializes in cancer and its treatment^[18].

Get adequate rest. Good sleep is important for health and well-being. Sleep problems are common in people with any type of cancer. If you have trouble sleeping, let your doctor or therapist know, as they may offer strategies or medicine to help^[18].

Set boundaries and practice self-care. It’s okay to say no when you’re not feeling up to something. Take time for activities that help you feel relaxed and fulfilled, whether that’s reading, meditating, taking a bath, or simply resting^[18].