AstraZeneca and Daiichi Sankyo's Enhertu Secures Landmark FDA Approval for HER2-Ultralow Breast Cancer

AstraZeneca and Daiichi Sankyo have achieved a significant milestone in breast cancer treatment with the U.S. Food and Drug Administration's (FDA) approval of Enhertu for patients with HER2-low or HER2-ultralow metastatic breast cancer. This latest endorsement, marking Enhertu's seventh FDA nod, positions the antibody-drug conjugate (ADC) as a potential new standard of care in hormone receptor-positive breast cancer treatment.

Expanding Enhertu's Reach in Breast Cancer Treatment

The FDA's decision allows Enhertu to be used earlier in the treatment sequence, following disease progression after one or more endocrine therapies. This approval is based on results from the DESTINY-Breast06 trial, which demonstrated a 36% reduction in the risk of disease progression or death compared to chemotherapy. Patients treated with Enhertu showed a median progression-free survival of 13.2 months, surpassing the 8.1 months observed in the chemotherapy group.

Dr. Aditya Bardia, a trial investigator from UCLA Health Jonsson Comprehensive Cancer Center, emphasized the significance of this approval, stating, "Enhertu offers a potential new standard of care for patients with HR-positive, HER2-low or HER2-ultralow metastatic breast cancer following endocrine therapy."

Redefining HER2 Expression in Breast Cancer

This latest approval underscores the importance of viewing HER2 expression beyond binary positive or negative terms. AstraZeneca estimates that up to two-thirds of hormone receptor-positive breast cancers typically classified as HER2-negative actually have low levels of the protein, with an additional 20% to 25% potentially having "ultralow" HER2 expression.

Krissa Smith, vice president of education at Susan G. Komen, highlighted the critical nature of this development, saying, "It is critical for patients to understand the HER2 status of their metastatic breast cancer to help them make informed treatment decisions."

Financial Implications and Future Prospects

Enhertu's expanding indications have translated into significant financial success. The drug achieved blockbuster status in 2022 and generated $2.7 billion in the first three quarters of 2024, up from $1.8 billion in the same period of 2023. This latest approval triggers a $175 million milestone payment from AstraZeneca to Daiichi Sankyo.

Looking ahead, AstraZeneca and Daiichi Sankyo are evaluating Enhertu in earlier stages of HER2-positive breast cancer, with Phase 3 trials ongoing in first-line settings and before or after surgical tumor removal. Results from these trials are anticipated later this year, potentially further solidifying Enhertu's position in breast cancer treatment.