Breast Cancer

What is biomarker testing?

Biomarker testing is a powerful tool that plays a critical role in understanding and guiding treatment decisions for metastatic breast cancer.

Biomarkers are specific characteristics of cancer cells, such as proteins or changes in tumor cell DNA, that provide information on how the cancer behaves.

In metastatic breast cancer, biomarker tests are often done to look for specific cancer cell features, including:

  • Proteins, such as estrogen receptors
  • Changes in tumor cell DNA, such as PIK3CA mutations

Why is biomarker testing important in metastatic breast cancer?

Over time, metastatic breast cancer can evolve, and its biomarkers may change. If you have been diagnosed with metastatic breast cancer, biomarker testing can help you and your healthcare team:

  • Understand more about what may be causing the cancer cells to grow and multiply
  • Choose effective treatments that target specific biomarkers
  • Monitor the cancer for biomarker changes that can help you decide on new treatment options
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Researchers continue to work on finding new treatments that target known and new biomarkers.

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When to ask your doctor about biomarker testing

Ask about biomarker testing whenever you and your doctor are discussing a new treatment plan, such as:

  • Soon after a metastatic breast cancer diagnosis
  • If cancer progresses (grows or spreads)

Getting tested at these times can help you and your healthcare team understand whether a certain treatment is working well or if the plan should be adjusted. This helps ensure that the treatment plan remains as effective as possible in controlling the cancer.

How is biomarker testing done?

Biomarker tests for metastatic breast cancer can be performed using a biopsy—a procedure that removes a small sample of tumor tissue—or a blood test, often called a liquid biopsy, that can look for DNA in the blood that has been shed by tumor cells.

The tumor tissue or blood is then sent to a laboratory for testing.

Testing Questions

Your step-by-step guide to biomarker testing

Step 1 — Take stock

Metastatic breast cancer biomarkers are highly individual. Understanding the cancer’s biomarker status is an important first step in your journey. This knowledge can help you feel confident and prepared to speak with your doctor moving forward.

Step 2 — Talk

Your doctor may have already had the cancer tested for biomarkers. It’s important to know which biomarker tests have already been performed and which ones are recommended for you. You have the right to know and understand your test results—they are key to understanding your diagnosis and treatment options.

These results are also important if you ever decide to seek a second opinion about your diagnosis or treatment plan.

Step 3 — Test

Your doctor will order testing for all recommended biomarkers. Some testing methods can check for one specific biomarker, and others can check for hundreds of biomarkers at a time. Depending on the type of test performed, it may take one to several weeks to receive results.

Step 4 — Treat

Based on your test results, your healthcare team will talk with you about the most effective treatment options for you, tailored to the specific biomarkers of the cancer and your overall health history.

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Disscussion Guide
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Megan O'Neil

Hear from Megan O'Neil

“I speak about biomarker testing so others will explore their options. As a young woman, I'm proof that your journey doesn’t end at diagnosis. It's the beginning of a new phase where understanding your options can make all the difference.”

Megan O'Neil

Megan's Story

At 30, Megan was thriving in her acting career and feeling optimistic about her future when she received a diagnosis of early-stage breast cancer. After chemotherapy, radiation, a double mastectomy, and hormone-lowering medication, she spent nearly five years free from cancer. Then, a sudden chest cramp signaled a devastating discovery: her breast cancer had returned, this time metastatic.

Megan worked closely with her healthcare team to navigate this new chapter. She began with one clinical trial and switched to another after seven months, a move that has proven beneficial. Recently, she underwent biomarker testing to gain deeper insights into her cancer and learned she carries the PIK3CA mutation—information that could offer her more treatment options in the future. Recognizing the significance of this, Megan wishes she had undergone biomarker testing at the time of her initial diagnosis.

Today, Megan continues to be closely monitored by her medical team and feels confident that her recent biomarker testing will help expand her treatment options and guide her path forward. As a passionate advocate, she now shares her journey to educate others facing similar challenges, underscoring the importance of biomarker testing in making informed decisions about care.

Betty Sanchez

Hear from Betty

“Seeking a second opinion was crucial after my misdiagnosis. Though challenging, it led me to my new healthcare team, who reviewed my pathology report and told me I have HER2-positive breast cancer. This guided me to an effective targeted treatment and fuels my advocacy to empower others in their healthcare decisions.”

Betty Sanchez

Betty's Story

Betty is an eight-year metastatic breast cancer thriver who learned early on the importance of advocating for herself. Initially dismissed as an insect bite, Betty's inflammatory breast cancer went undetected until her mother, a retired nurse, insisted on a second opinion.

While this led to a correct diagnosis of metastatic breast cancer, it also prompted immediate, aggressive treatment that took a toll on Betty's physical, emotional and mental state. Fortunately, her journey took a more hopeful turn when she had a second opinion and learned her cancer as HER2-positive, a subtype that responded well to a treatment that was less toxic and more targeted.

Biomarker testing has never been discussed with Betty and she plans to ask her doctor at her next appointment if this is something she should consider.

Now living in Puerto Rico, Betty passionately advocates for patients to be informed advocates for their cancer care. Knowing the sub-type of breast cancer is critical and asking about biomarker testing may reveal other treatment options. Inspired by her journey from misdiagnosis to informed advocacy, Betty empowers others to take an active role in navigating their treatment plans, ensuring they receive the personalized care they deserve.

Stay informed with the latest news on biomarker testing for metastatic breast cancer

Share your story

Promote biomarker testing awareness in metastatic breast cancer.

Create your own sign or download and print the sign below, adding your biomarker. Then:

  • Take a selfie with the sign, or just a photo of the sign if you prefer
  • Share the photo on your social media, along with your story about the impact that biomarker testing had on your treatment
  • Add the hashtag #NoOneMissed to your social post
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About No One Missed

No One Missed is a community-led campaign driven by LUNGevity Foundation in addition to support from patient advocacy and industry partners. The campaign’s mission is to build public awareness of comprehensive biomarker testing as a critical part of cancer diagnosis and empower patients to discuss comprehensive biomarker testing with their healthcare team. The No One Missed: Metastatic Breast Cancer campaign was launched in partnership with Living Beyond Breast Cancer.

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We envision a future that ensures there’s No One Missed when it comes to biomarker testing in metastatic breast cancer. It’s a critical step to getting a fully informed diagnosis.

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