(BPT) - Southern California native Lisa Shoemaker has been coping with breast cancer for a long time, and one thing keeps her going: her family. She married her high school sweetheart and had two boys before she was first diagnosed with stage 2 breast cancer at age 29. With this devastating diagnosis, Shoemaker feared she wouldn't live to see her 2- and 4-year-old sons grow up.

That was 26 years ago.

Through all these years, Shoemaker has been motivated to keep going because of her love for her family - first her husband and sons, and now her three grandchildren, too.

While her initial treatment for the stage 2 breast cancer was intense and extensive, it provided stability for nearly a decade until a routine mammogram and subsequent MRI revealed that her cancer had returned. She went through treatment again, including surgery and hormone therapy, but after all she had endured, Shoemaker decided to undergo a preventative double mastectomy. With her cancer again stable, she was able to continue raising her children through their high school years and live life as she normally would.

But unfortunately, that was not the end of her cancer story. At age 45, and several years after her preventative double mastectomy, Shoemaker experienced pain in her shin, which she initially attributed to increased exercise. When her pain could no longer be ignored, she sought medical attention. An orthopedic doctor immediately sent her to the hospital after telling her that her cancer had likely metastasized to her bones.

After meeting with specialists, she had surgery to remove a tumor in her tibia which had caused it to fracture. Shoemaker was then diagnosed with metastatic breast cancer (mBC) and told she had about two years to live.

What is metastatic breast cancer?

When someone has mBC, that means the cancer is considered to be stage 4 and has spread to other parts of the body. While mBC has no cure, according to the National Breast Cancer Foundation, people with mBC have been able to live longer by managing it as a chronic illness with continuous treatment and monitoring.

For those living with ER+/HER2- metastatic breast cancer - the most common subtype of mBC - the first treatment is often a hormone therapy taken alone or in combination with a CDK4/6 inhibitor. But over time the cancer changes and mutates to try and "outsmart" the treatment, and these mutations can cause tumors to stop responding to certain therapies.

A specific mutation, called an ESR1 mutation, is an example of one mutation that may cause treatment to stop working, which can lead to disease progression and tumor growth. An ESR1 mutation develops as a result of previous exposure to endocrine, or hormone, therapy. Nearly 50% of people with ER+/HER2- metastatic breast cancer may develop an ESR1 mutation, which in turn can cause their disease to progress.

If you live with ER+/HER2- mBC, knowing whether this mutation is present can provide important information to help your health care team understand what other kinds of treatment options may be appropriate. This is why it is vital to ask your doctor about ESR1 mutation testing whenever mBC progresses.

ESR1 mutations are most likely to be found when:

• A person's metastatic breast cancer has progressed (spread, grown or worsened) while on hormone therapy
• The current hormone therapy is no longer working
• The person has taken a hormone therapy for a year or more
• The person has taken multiple hormone therapies

"Unfortunately, for the majority of patients living with metastatic breast cancer, treatments eventually stop working," said Dr. Aditya Bardia, Director, Breast Oncology Program, UCLA Health Jonsson Comprehensive Cancer Center, "which means, if possible, ESR1 mutation testing should be considered at every point of progression of the disease, as it might open doors for additional treatment options. We know that ESR1 mutations are acquired and serial testing might pick up mutations that are not present initially."

This is exactly what happened to Lisa Shoemaker, as she had already been through several rounds of chemotherapy and hormone therapies after living with mBC for over 10 years. Shoemaker had regular scans and tests done to monitor her cancer. One of those was a blood test which found that the ESR1 mutation was present, and indicated a different treatment could potentially help manage the progression and spread of her cancer.

Thanks to this important information, Shoemaker's health care team was able to adjust how they were treating her mBC. ESR1 mutation testing enabled her oncologist to tailor her treatment appropriately. Best yet, she can spend time with her grandchildren, which is one of the greatest joys in her life.

"I am so thankful that I'm able to help raise my grandchildren, not only to be alive to see them, but also to be present in their lives. I feel a sense of normalcy again," said Shoemaker. "My grandchildren are the light of my life and motivate me. They are my reason to keep on keeping on."

Because the ESR1 mutation can develop at any time during treatment, it's essential to be retested for this mutation at every point of mBC disease progression throughout the treatment journey. If you or a loved one has ER+/HER2- metastatic breast cancer, ask your health care provider about being tested for the ESR1 mutation. Testing for an ESR1 mutation can be done via a blood test and does not require a tissue biopsy.

Learn more at mBCTesting.com.