Highlights
- Trastuzumab deruxtecan (T-DXd) reduced the risk of invasive disease recurrence or death by 53% compared to trastuzumab emtansine (T-DM1).
- The 3-year invasive disease-free survival (iDFS) rate was 92.4% for the T-DXd group versus 83.7% for the T-DM1 group.
- The benefit of T-DXd was consistent across key secondary endpoints, including disease-free survival and distant recurrence-free survival.
- Interstitial lung disease (ILD) remains a critical safety concern, occurring in 9.6% of patients treated with T-DXd, necessitating rigorous clinical monitoring.
The Unmet Need in Residual HER2-Positive Breast Cancer
The landscape of HER2-positive (HER2+) early breast cancer has been transformed by neoadjuvant systemic therapies. Achieving a pathologic complete response (pCR) following neoadjuvant treatment is a strong predictor of favorable long-term outcomes. However, a significant proportion of patients do not achieve pCR and have residual invasive disease at the time of surgery. These patients face a substantially higher risk of disease recurrence and death.
For several years, the standard of care for patients with residual disease has been trastuzumab emtansine (T-DM1), based on the landmark KATHERINE trial, which showed improved outcomes over trastuzumab alone. Despite this advancement, many patients still experience recurrence, particularly those with high-risk features such as node-positive disease or large residual tumor burdens. There has been an urgent clinical need for more potent therapeutic options to further reduce the risk of relapse in this high-risk population.
DESTINY-Breast05: Study Design and Participant Characteristics
The DESTINY-Breast05 trial (NCT04622319) was a phase 3, open-label, randomized, international study designed to evaluate whether trastuzumab deruxtecan (T-DXd) could provide superior outcomes compared to T-DM1 in the postneoadjuvant setting. T-DXd is a next-generation antibody-drug conjugate (ADC) comprising a humanized anti-HER2 IgG1 monoclonal antibody, a cleavable tetrapeptide-based linker, and a potent topoisomerase I inhibitor payload.
Study Population and Randomization
The trial enrolled 1,635 patients with HER2-positive breast cancer who had residual invasive disease in the breast or axillary lymph nodes after completing at least six cycles of neoadjuvant therapy (including HER2-targeted agents). Specifically, the study targeted a high-risk cohort: patients with node-positive disease at the time of surgery or those with inoperable disease at diagnosis. Participants were randomized in a 1:1 ratio to receive either T-DXd (5.4 mg/kg) or T-DM1 (3.6 mg/kg) intravenously every three weeks.
Endpoints
The primary endpoint was invasive disease-free survival (iDFS), defined as the time from randomization to the date of first occurrence of ipsilateral invasive breast tumor recurrence, ipsilateral regional invasive breast cancer recurrence, distant recurrence, contralateral invasive breast cancer, or death from any cause. Key secondary endpoints included disease-free survival (DFS), overall survival (OS), and safety.
Efficacy Results: A New Benchmark for Survival
The results of DESTINY-Breast05 represent a potential paradigm shift in the management of high-risk early breast cancer. At the median follow-up of approximately 30 months, the efficacy data favored T-DXd across all primary and secondary measures.
Invasive Disease-Free Survival (iDFS)
In the T-DXd group, 51 patients (6.2%) experienced an iDFS event, compared to 102 patients (12.5%) in the T-DM1 group. This translated to a hazard ratio (HR) of 0.47 (95% confidence interval [CI], 0.34 to 0.66; P < 0.001). The 3-year iDFS rates were 92.4% for T-DXd and 83.7% for T-DM1, reflecting an absolute improvement of 8.7 percentage points. This 53% reduction in the risk of invasive recurrence or death is clinically profound, especially considering that T-DM1 was already a highly effective standard of care.
Secondary Outcomes
The benefit extended to disease-free survival, with a hazard ratio of 0.47 (95% CI, 0.34 to 0.66). The 3-year DFS rate was 92.3% in the T-DXd arm versus 83.5% in the T-DM1 arm. Furthermore, T-DXd showed promising trends in reducing distant recurrences, which are the primary drivers of breast cancer mortality. While overall survival data are still maturing, the early divergence of the survival curves suggests a robust long-term benefit for the T-DXd cohort.
Safety Profile and the Management of Adverse Events
While the efficacy of T-DXd is superior, the safety profiles of the two ADCs differ significantly, necessitating distinct clinical management strategies.
Common Toxicities
Patients receiving T-DXd reported higher rates of gastrointestinal and hematologic toxicities. The most frequent adverse events in the T-DXd group were nausea (71.3%), constipation (32.0%), and vomiting (31.0%). Decreased neutrophil counts (31.6%) were also common. In contrast, T-DM1 was more frequently associated with laboratory abnormalities, specifically increased levels of aspartate aminotransferase (50.2%) and alanine aminotransferase (45.3%), along with decreased platelet counts (49.8%).
Interstitial Lung Disease (ILD)
The most significant safety concern for T-DXd is drug-related interstitial lung disease or pneumonitis. In DESTINY-Breast05, adjudicated drug-related ILD occurred in 9.6% of patients in the T-DXd group, compared to 1.6% in the T-DM1 group. Most ILD events were low-grade (Grade 1 or 2); however, two fatal cases (Grade 5) occurred in the T-DXd arm. This highlights the absolute necessity for clinicians to maintain a high index of suspicion for respiratory symptoms and to adhere strictly to management guidelines, which include immediate treatment interruption and the initiation of corticosteroids for any suspected ILD.
Expert Commentary: Clinical Implications and Practice Shifts
The DESTINY-Breast05 trial is likely to establish T-DXd as the preferred postneoadjuvant treatment for high-risk patients with residual HER2+ disease. The biological rationale for T-DXd’s superior efficacy lies in its high drug-to-antibody ratio (approximately 8) and its membrane-permeable payload, which allows for a “bystander effect.” This effect is particularly useful in residual disease, which may exhibit heterogeneous HER2 expression.
However, the transition from T-DM1 to T-DXd in the early-stage setting requires careful consideration of the risk-benefit ratio. For patients with very low-volume residual disease (e.g., isolated tumor cells or micrometastases only), the benefit of T-DXd over T-DM1 may be less pronounced, and the risk of ILD might weigh more heavily in the decision-making process. Conversely, for the high-risk population studied in this trial—those with node-positive disease—the absolute benefit of nearly 9% in iDFS is compelling.
Clinicians must also consider the “financial toxicity” and the infrastructure required for the intensive monitoring associated with T-DXd. Regular CT imaging and proactive management of nausea are essential components of the T-DXd treatment protocol that may differ from previous experiences with T-DM1.
Conclusion
The DESTINY-Breast05 trial marks a significant milestone in breast cancer research. By demonstrating a 53% reduction in the risk of recurrence compared to the previous standard of care, T-DXd has set a new benchmark for efficacy in the postneoadjuvant setting for HER2-positive early breast cancer. While the risk of interstitial lung disease requires vigilant clinical oversight, the substantial improvement in invasive disease-free survival offers a new level of hope for patients at high risk of recurrence. Future research will likely focus on identifying biomarkers to further refine patient selection and exploring the use of T-DXd in even earlier lines of therapy.
Funding and ClinicalTrials.gov
The DESTINY-Breast05 trial was funded by Daiichi Sankyo and AstraZeneca. The clinical trial registration number is NCT04622319.
References
Loibl S, Park YH, Shao Z, et al. Trastuzumab Deruxtecan in Residual HER2-Positive Early Breast Cancer. N Engl J Med. 2025 Dec 10. doi: 10.1056/NEJMoa2514661. Epub ahead of print. PMID: 41370739.
von Minckwitz G, Huang CS, Mano MS, et al. Trastuzumab Emtansine for Residual Invasive HER2-Positive Breast Cancer. N Engl J Med 2019;380:617-628.
Modi S, Jacot W, Yamashita T, et al. Trastuzumab Deruxtecan in HER2-Low Advanced Breast Cancer. N Engl J Med 2022;387:9-20.
