FDA expands Enhertu into HER2-positive early breast cancer: full analysis

AstraZeneca and Daiichi Sankyo’s Enhertu has won a major expansion in the US, moving from advanced disease into curative-intent treatment for HER2-positive early-stage breast cancer. On May 15, 2026, the FDA approved two separate indications: neoadjuvant use before surgery in adults with Stage II or III HER2-positive disease, and adjuvant use after surgery in adults with residual invasive disease following neoadjuvant therapy. The agency also approved two companion diagnostic assays alongside the label expansion. (fda.gov)

The approval builds on a broader shift already underway in breast oncology. Enhertu, an antibody-drug conjugate jointly developed by Daiichi Sankyo and AstraZeneca, first established itself in metastatic HER2-positive breast cancer and later expanded into HER2-low and HER2-ultralow disease in advanced settings. The new FDA action pushes the drug into much earlier treatment, where the goal is cure rather than disease control. Company materials had already signaled momentum: Daiichi Sankyo said in March 2026 that China had granted the first global approval for neoadjuvant use in this curative-intent setting, while the European Medicines Agency validated an application in February 2026 for post-neoadjuvant use after residual disease. (fda.gov)

For the neoadjuvant indication, the FDA relied on DESTINY-Breast11, a randomized phase 3 trial in 927 adults with high-risk HER2-positive early-stage breast cancer. Patients who received four cycles of Enhertu followed by THP achieved a 67.3% pathologic complete response rate, compared with 56.3% for those treated with dose-dense doxorubicin/cyclophosphamide followed by THP, a statistically significant improvement. Still, the FDA noted that event-free survival and overall survival were not statistically controlled or powered in that analysis, and supportive evidence came from the separate adjuvant trial. (fda.gov)

For the adjuvant indication, the supporting study was DESTINY-Breast05, which enrolled 1,635 adults with HER2-positive breast cancer and residual invasive disease after neoadjuvant therapy. In that trial, Enhertu outperformed trastuzumab emtansine, or T-DM1, with a 3-year invasive disease-free survival rate of 92.4% versus 83.7%, corresponding to a hazard ratio of 0.47. The FDA label also carries a boxed warning for interstitial lung disease and pneumonitis, plus warnings for neutropenia and left ventricular dysfunction, which will remain central to treatment selection and monitoring. (fda.gov)

Industry and oncology commentators are already framing the move as potentially practice-defining, though not without debate. The ASCO Post reported that DESTINY-Breast05 positions Enhertu as a possible new standard of care in the post-neoadjuvant setting for patients with residual disease. At the same time, a separate ASCO Post expert discussion highlighted a key open question in early 2026: whether Enhertu is best used before surgery, after surgery, or selectively in one setting over the other, especially because the neoadjuvant survival data remain immature. That tension is likely to shape guideline discussions and sequencing decisions. (ascopost.com)

Why it matters: For veterinary professionals, the direct clinical impact is limited, but the strategic relevance is real. Comparative oncology continues to borrow concepts from human cancer care, and this approval highlights three trends worth tracking: antibody-drug conjugates are moving earlier in treatment pathways, biomarker testing is increasingly inseparable from therapy selection, and regulators appear willing to accept strong pathologic complete response data when paired with supportive evidence from adjacent settings. For veterinary oncologists, academic centers, and industry teams watching translational platforms, Enhertu’s expansion is another sign that targeted, biomarker-defined oncology is getting more precise, more complex, and more dependent on coordinated diagnostics and toxicity management. (fda.gov)

What to watch: The next milestones will be guideline uptake, international regulatory decisions through Project Orbis partner agencies and Europe, real-world tolerability in earlier-stage patients, and longer-term event-free and overall survival data that could settle the debate over where Enhertu fits best in the HER2-positive early breast cancer pathway. (fda.gov)