What Is HER2+ Metastatic Breast Cancer?

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Breast cancer is a disease in which cells in the breast begin to grow uncontrollably. These abnormal cells can start growing in either the ducts or in the lobules of the breasts. When cancer becomes metastatic, it moves from its original location to other areas of the body through the bloodstream or lymphatic system. One of the important facts to know about your breast cancer is whether it is HER2-positive. 

About 20% of all breast cancers are HER2-positive. HER2 (human epidermal growth factor receptor 2) is a protein on the outside of all cells of the breast, which tells them to grow. Some breast cancer cells have too many HER2 proteins, which is one of the reasons they grow uncontrollably. Knowing if breast cancer is HER2-positive or not helps the oncology team come up with the best treatment plan. 

This article will review the symptoms of metastatic HER2-positive breast cancer, the causes, as well as how it is diagnosed and treated. 

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HER2+ Metastatic Breast Cancer Symptoms

The symptoms of HER2-positive metastatic breast cancer are no different than if the cancer was not HER2-positive. Symptoms of metastatic cancer can vary depending upon where the cancer is located and include:

  • Breasts: If cancer starts in the breast, there may be a lump in the breast that can be felt. There can also be swelling under the armpit. 
  • Brain: Symptoms of cancer that has spread to the brain include headaches, dizziness, vision changes, confusion, and loss of balance. 
  • Bones: Cancer that has spread to the bones may cause pain to the affected bones or joints, or the bones may break. 
  • Lungs: Cancer that spreads to the lungs may cause chest pain, shortness of breath, or cough. 
  • Liver: Metastatic cancer in the liver may cause abdominal pain, swelling in the abdomen, itching of the skin, yellowing of the eyes or skin, or nausea. 

Other general symptoms of breast cancer that has spread may include poor appetite, weight loss, and increased fatigue. 

What Causes HER2+ Breast Cancer?

Breast cancer starts when the cells in the ducts or the lobules of the breast begin to grow uncontrollably, due to the DNA in the cell becoming abnormal.

As part of this abnormal process, sometimes these cells have too many HER2 proteins on the outside of the cells. This extra HER2 protein tells the cells to keep growing, even though they shouldn’t be. As this process continues, a mass in the breast forms, and over time, it can begin to grow and spread into other areas of the body.

It is not often known what the trigger is that alters the DNA inside the cell to become abnormal. There are, however, some gene mutations that have been shown to increase someone’s risk of developing cancer. Though not the only ones, two of these genes are BRCA1 and BRCA2. These genes can be passed down through family members, and the person who gets them has a higher risk of getting breast cancer.

Besides genetics, there are other factors that have been found to increase the risk of developing breast cancer. These risk factors include:

  • Increasing age
  • Having dense breasts
  • Starting menstrual cycles at a younger age
  • Having never given birth
  • Starting menopause at a later age
  • Taking hormone therapy
  • History of radiation to the breast or chest
  • Being obese
  • High alcohol intake

How HER2+ Breast Cancer Is Diagnosed

There are many steps in the process of diagnosing breast cancer. 

If a person has a symptom that is concerning to them, such as a lump in their breast, they should discuss it with their healthcare provider. The healthcare provider will likely start by taking a medical history and performing a physical exam. This can help them determine what is causing the symptoms. The next step in the process is imaging. 

Imaging Tests

A mammogram is often one of the first tests that can be performed, especially if there is a concerning finding in the breast exam. Mammograms are typically recommended for most people with breasts once a year, and breast cancer is sometimes found during a routine screening.

If you have a lump in your breast and it's been a while since your last mammogram, your healthcare provider may recommend this test to get a better look at the mass.

If cancer is suspected to be in other areas outside of the breasts, additional imaging will be done of the body as a whole. These imaging tests may include an MRI (magnetic resonance imaging), CT (computed tomography) scan, or PET (positron-emission tomography) scan.


A biopsy is a procedure that removes tissue from the suspicious area and tests it to see if there are cancer cells present. The biopsy may be done of suspicious breast cancer as well as in other areas of the body where suspicious cells may be, such as the bones, lungs, or liver. Once cancer cells have been found, additional tests will help characterize the breast cancer. 

HER2 status is important to know. If breast cancer is HER2-positive, this means there are a lot of HER2 proteins being made in your body that are causing the cancer to continue to grow. 

Other tests include looking for estrogen and progesterone receptors on the cancer cells. If these tests are positive, it means the breast cancer is using estrogen and progesterone as fuel to continue growing.

Treatment Options for HER2+ Breast Cancer

If breast cancer is HER2-positive, there are targeted medications that can treat that type of breast cancer specifically. The order in which these medications are used may be different for each person, depending on any previous therapy the patient has had.

These medications may also be used in combination with each other or with chemotherapy medications, including those in the list that follows.

Herceptin (trastuzumab)

Herceptin is an infusion of a monoclonal antibody that blocks the HER2 cells from receiving signals to keep growing. 

Perjeta (pertuzumab)

Perjeta works much like Herceptin to block HER2 cells from continuing to grow. It is often used in combination with Herceptin.

Tykerb (lapatinib)

Tykerb comes in pill form and works by blocking some of the proteins that HER2-positive cells need to keep growing. 

Kadcyla (trastuzumab emtansine) 

Kadcyla is a combination of chemotherapy medication and a HER2 targeted drug that is given by infusion. It works by using the HER2 medication to move chemotherapy into the cells.

Enhertu (fam-trastuzumab-deruxtecan-nxki)

In a similar way as Kadcyla, Enhertu binds a HER2 targeted medication with chemotherapy. It then carries the chemotherapy into the HER2-positive cancer cells. 

Other treatments

In addition to the above medications, chemotherapy or other cancer therapies may be given. Other therapy, such as surgery or radiation, may be used to treat specific areas. 

Prognosis for Metastatic HER2+ Cancer

Generally, when breast cancer becomes metastatic, it is not possible to cure the cancer. This does not mean that the cancer isn’t treatable, though. Data from the National Cancer Institute estimates that for those diagnosed with metastatic breast cancer, 29% have a five-year survival rate. This means that 29% of the people with that cancer are still alive in five years. 

Coping With Your Diagnosis

Being diagnosed with metastatic HER2-positive breast cancer can cause a lot of feelings. It is a life-altering diagnosis, and feelings can range from fear to anger. Finding support from friends or family can be important as you go through the steps of diagnosis and treatment. There are many support groups, both in person and virtual, as well as many websites with helpful information in navigating this journey. 


HER2-positive metastatic breast cancer is a type of breast cancer that has spread to areas of the body outside of the breasts. These cancer cells have many HER2 receptors, which lead to the cancer cells being able to grow out of control.

It is diagnosed through imaging studies and a biopsy. Treatment can vary but typically includes HER2 targeted therapy, as well as chemotherapy, and possibly radiation or surgery. 

A Word From Verywell 

A diagnosis of HER2-positive metastatic breast cancer is life changing. Feelings of fear of the future and the unknown are natural and dealing with treatment side effects can be very stressful.

You'll need a strong support team around you throughout this journey, so be sure to reach out to your loved ones and seek out a support group. If you ever have any questions or concerns, be sure to discuss them with your treating physician. It’s so important for you to be a part of your healthcare decisions.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. CDC. What is breast cancer?

  2. American Cancer Society. Breast cancer HER2 status.

  3. Cancer.Net. Breast cancer- metastatic.

  4. Medline Plus. Breast Cancer.

  5. Breastcancer.org. HER2 status.

  6. National Cancer Institute. Cancer stat facts- female breast cancer.

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.