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More Metastatic Breast Cancer Patients May Qualify for an FDA-Approved Infusion Treatment

More metastatic breast cancer patients may be eligible to receive a treatment recently approved by the U.S. Food and Drug Administration (FDA) for a newly defined category called “HER2-low” metastatic breast cancer. 

Enhertu (trastuzumab deruxtecan) is the first approved I.V. infusion for the treatment of patients with unresectable (unable to be removed) or metastatic (spread to other parts of the body) “HER2-low” breast cancer. The groundbreaking new treatment by drugmaker AstraZeneca is showing improvements for women with the newly-defined subtype — HER2-low — “in both progression-free survival and overall survival,” the FDA states.


“The approval of (Enhertu) for the treatment of metastatic HER2-low breast cancer will have a significant positive impact on a large percentage of patients,” Reshma Mahtani, D.O., chief of breast oncology at Baptist Health Miami Cancer Institute. “This is the first approved therapy for HER2-low breast cancer and will provide an important new targeted therapy option for many patients given the improvements demonstrated over standard chemotherapy options.”

HER2 receptors, which are proteins made by the HER2 gene, are important in determining a patient’s breast cancer treatment. HER2-negative includes hormone-receptor positive and triple-negative breast cancers. HER2-low, the new classification of the HER2 subtype, has low level HER2 protein expression on the cell surface, but not enough to be classified as HER2-positive.

The FDA’s approval followed a nationwide clinical trial that enrolled 557 adult patients with unresectable or metastatic HER2-low breast cancer. The median age of trial participants was 57 years old, ranging from 28 to 81 years of age.

“This new study looked at patients who had ‘any’ amount of HER2 measurable, not the full amount positive,” explains Louise E. Morrell, M.D., medical director of Lynn Cancer Institute at Boca Raton Regional Hospital. “So, if their tumor tests showed that a patient’s cancer cells had any amount, they could benefit from this new treatment. The benefit was truly significant and represents a whole new treatment for women with metastatic breast cancer.”


Patients with HER2-low breast cancer are eligible for Enhertu if they have received at least one prior chemotherapy in the metastatic setting, or their cancer returned during, or within 6 months of completing, adjuvant chemotherapy, according to the FDA.

“Women who today have breast cancer and the treatment is not working well, can go back to the pathology or be biopsied again, and tested to see if they meet the criteria for this new drug,” explains Dr. Morrell. “The excitement is also in part because this new result will allow additional studies to determine if this treatment can also be used either before surgery or after surgery — and prevent recurrence of breast cancer from ever happening.”

In the 1990s, researchers discovered that breast cancer had high levels of HER2 receptors, said Dr. Morrell. The benefits of giving an antibody that blocks that receptor spurred advancements of treatments. The findings at the time were that the drug (Herceptin) only worked if the patient had a positive HER2 test. “This remains true to this day, and one of the most important advances toward curing patients with breast cancer who have this particular characteristic,” said Dr. Morrell. “But the treatment did not appear to have any affect unless you have this high HER2 score.” 

However, in the case of Enhertu, she adds, “the low levels of receptor are enough to target the cells and get the anti-cancer drug into the cancer cells specifically.”

 Approximately 80 to 85 percent of new breast cancer cases were previously considered to be HER2-negative subtype (including hormone receptor-positive and triple-negative breast cancer), the FDA states.  Of that proportion of breast cancer diagnoses, about 60 percent of patients previously classified as having HER2-negative subtype can now be considered as HER2-low, the FDA adds.

“Having therapies that are specially tailored to each patient’s cancer subtype is a priority to ensure access to safe and innovative treatments,” stated Richard Pazdur, M.D., director of the FDA’s Oncology Center of Excellence, in a news release.

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With internationally renowned centers of excellence, 12 hospitals, more than 27,000 employees, 4,000 physicians and 200 outpatient centers, urgent care facilities and physician practices spanning across Miami-Dade, Monroe, Broward and Palm Beach counties, Baptist Health is an anchor institution of the South Florida communities we serve.

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