First Targeted Therapy for HER2-Low Breast Cancer Approved by FDA

On August 5, U.S. Food and Drug Administration (FDA) approved Enhertu (fam-trastuzumab-deruxtecan-nxki). Enhertu, an IV infusion, treats patients with unresectable or metastatic HER2-low breast cancer. It is the first therapy approved by the FDA for the targeted treatment of this subset of breast cancer.

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What is HER2-low Breast Cancer?

HER2 proteins are receptors on breast cells. They usually control how breast cells grow, develop, and repair themselves. However, when the gene controlling this protein fails to function correctly, too many copies are produced. This leads to some types of breast cancer.

HER2-low breast cancer is a subset of HER-2 negative breast cancer, a type of cancer containing low levels of HER2. The newly defined subset means that, despite still having lower than average levels of the HER2 protein, there is still enough for it to be targetable in treatments. 

Enhertu uses the levels of HER2 in the low subsets to combat it. Upon administration of trastuzumab, the antibody within Enhertu attaches to the HER2 receptor on the cancer cells. Next, the chemotherapy factor of the treatment, known as deruxtecan, releases and destroys the attached cancer cells and any surrounding targeted cells.

Clinical Trial Results Wins FDA Approval 

The FDA based its approval on the results of the DESTINY-Breast04 clinical trial. This randomized, multicenter, open-label clinical trial enrolled 557 adult patients with unresectable or metastatic HER2-low breast cancer. Of the total patients, 373 receive Enhertu via an IV infusion. The other 187 received alternative chemotherapy options. These included eribulin, capecitabine, gemcitabine, nab paclitaxel or paclitaxel.

Overall, patients infused with Enhertu saw more significant improvement in progression-free and overall survival than patients who received alternative treatment. However, patients who received the Enhertu treatment reported side effects such as nausea, fatigue, alopecia, vomiting, constipation, decreased appetite, musculoskeletal pain, and diarrhea.

Despite the side effects, the FDA granted the targeted therapy approval four months before the Prescription Drug User Fee Act (PDUFA) deadline.
On the approval, Richard Pazdur, M.D., director of the FDA’s Oncology Center of Excellence and acting director of the Office of Oncologic Diseases in the FDA’s Center for Drug Evaluation and Research, said, “Today’s approval highlights the FDA’s commitment to be at the forefront of scientific advances, making targeted cancer treatment options available for more patients. Having therapies that are specially tailored to each patient’s cancer subtype is a priority to ensure access to safe and innovative treatments.”

Today marks the first targeted therapy for HER2-low breast cancer achieving approval by the FDA. Now, over 80% of patients with breast cancer have a new treatment designed explicitly for their subset of breast cancer.

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Author

Max Heirich