Update on Recent Breast Cancer Treatment Drug Enhertu New FDA Approval Expands Indications for Most Aggressive Form of HER2-positive Breast Cancer

The July Developments in Specialty Pharmacy discussed the potential benefit of Enhertu® (trastuzumab-deruxtecan) for patients who have HER2-low breast cancer. To update our readers, on August 5, 2022, the FDA approved an expanded indication for Enhertu making it the first therapy approved to treat unresectable or metastatic HER2-low breast cancer. It received Priority Review and Breakthrough Therapy designations for this indication and was approved four months ahead of the scheduled FDA review date which wasn’t expected until fourth quarter of this year.

It is estimated that almost 300,000 cases of breast cancer will be diagnosed in the United States during 2022. Historically breast cancer has been classified as HER-2 positive or negative depending on the amount of HER-2 receptors on the breast cancer cells. Approximately 60% of patients previously classified as having HER-2 negative subtype will now be considered HER2-low and therefore have a new treatment option available. Prior to Enhertu’s additional indication, HER2-low patients received endocrine therapy or chemotherapy, often with limited success.

The approval by the Food and Drug Administration (FDA) was based on the results from the DESTINY-Breast04 Phase III trial. In the primary endpoint analysis, Enhertu demonstrated:

• A 50% reduction in the risk of disease progression or death versus physician’s choice of chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel or nab-paclitaxel) in patients with HER2-low metastatic breast cancer with HR-positive disease.
• A median progression free survival (PFS) of 9.9 months was seen in patients treated with Enhertu compared to 5.1 months with chemotherapy.
• Results also demonstrated a 36% reduction in the risk of death with Enhertu compared to chemotherapy in patients with HR-positive disease with a median overall survival of 23.4 months with Enhertu versus 16.8 months with chemotherapy, meeting a key secondary endpoint of the trial.