Highlight
Trastuzumab deruxtecan combined with pertuzumab significantly prolongs progression-free survival (PFS) compared to the standard regimen of taxane, trastuzumab, and pertuzumab (THP) as first-line treatment in HER2-positive advanced or metastatic breast cancer. This combination achieves higher objective and complete response rates, with longer duration of response. Safety profiles are consistent with expectations, though interstitial lung disease (ILD) remains a notable risk requiring vigilance.
Study Background
HER2-positive breast cancer, characterized by overexpression of the human epidermal growth factor receptor 2 (HER2), accounts for approximately 15-20% of breast cancer cases. It is associated with aggressive tumor behavior and worse prognosis. Targeted HER2 therapies, such as trastuzumab and pertuzumab combined with chemotherapy, are the established first-line treatments for advanced disease, significantly improving outcomes. However, despite these advancements, resistance and disease progression remain common challenges, underscoring an unmet medical need for more effective first-line therapeutic options.
Trastuzumab deruxtecan is an antibody–drug conjugate (ADC) that links trastuzumab to a potent topoisomerase I inhibitor payload through a cleavable linker, enabling targeted delivery of chemotherapy to HER2-expressing cancer cells. It has demonstrated efficacy in previously treated HER2-positive metastatic breast cancer but its role as initial therapy in the metastatic setting was unestablished prior to the DESTINY-Breast09 study.
Study Design
DESTINY-Breast09 was a randomized, multicenter, phase 3 clinical trial enrolling patients with HER2-positive advanced or metastatic breast cancer who had not received prior chemotherapy or HER2-directed therapy for metastatic disease. The study randomized participants 1:1:1 to receive one of three interventions:
- Trastuzumab deruxtecan plus pertuzumab (experimental arm)
- Trastuzumab deruxtecan plus placebo (blinded; data pending)
- Taxane plus trastuzumab and pertuzumab (THP, standard of care)
The primary endpoint was progression-free survival (PFS) as assessed by blinded independent central review. Secondary endpoints included objective response rate (ORR), duration of response, and safety profiles.
Key Findings
This interim analysis reports results comparing trastuzumab deruxtecan plus pertuzumab with the THP standard regimen, with data cutoff on February 26, 2025. The trastuzumab deruxtecan plus placebo arm data remain blinded pending final PFS analysis.
Progression-Free Survival and Response Rates
The median PFS was markedly longer for the trastuzumab deruxtecan plus pertuzumab group at 40.7 months compared to 26.9 months in the THP group. The hazard ratio (HR) for progression or death was 0.56 (95% CI, 0.44 to 0.71; P < 0.00001), indicating a 44% reduction in risk and statistically significant superiority over THP.
Objective response rates were higher with trastuzumab deruxtecan plus pertuzumab at 85.1% versus 78.6% with THP. Complete response rates doubled, from 8.5% in the THP arm to 15.1% in the experimental arm. Furthermore, median duration of response extended significantly to 39.2 months compared to 26.4 months with THP.
Safety and Tolerability
The incidence of grade 3 or higher adverse events was comparable between groups: 63.5% in the trastuzumab deruxtecan plus pertuzumab arm versus 62.3% in the THP arm. Common severe adverse events with trastuzumab deruxtecan plus pertuzumab included neutropenia, hypokalemia, and anemia, while THP was more associated with neutropenia, leukopenia, and diarrhea.
A critical safety consideration is drug-related interstitial lung disease (ILD) or pneumonitis, which occurred in 12.1% of patients receiving trastuzumab deruxtecan plus pertuzumab (mostly grade 1 or 2), including two grade 5 events (fatalities). By contrast, ILD incidence was 1.0% with THP and non-fatal. These findings necessitate close monitoring and early management of pulmonary symptoms for patients on trastuzumab deruxtecan.
Expert Commentary
The DESTINY-Breast09 trial establishes trastuzumab deruxtecan plus pertuzumab as a robust first-line therapeutic alternative that significantly extends disease control compared to the current standard THP regimen. The magnitude of PFS improvement is clinically meaningful, potentially translating into prolonged survival and quality of life benefits for patients with HER2-positive metastatic breast cancer.
The dual antibody targeting approach—pertuzumab blocking HER2 dimerization and trastuzumab deruxtecan delivering potent cytotoxicity—may contribute to enhanced anti-tumor activity, overcoming some resistance mechanisms encountered in standard therapy.
However, the increased incidence of ILD highlights the critical need for vigilant pulmonary monitoring and risk stratification. Oncologists must balance efficacy benefits with potential pulmonary toxicity, tailoring treatment and ensuring prompt intervention upon any respiratory symptom onset.
Limitations of the report include pending data from the trastuzumab deruxtecan plus placebo arm, which will clarify the incremental value of combining pertuzumab with trastuzumab deruxtecan. Also, overall survival data remain immature and will be necessary to fully define the impact.
Conclusion
Trastuzumab deruxtecan combined with pertuzumab offers a promising, highly effective first-line option for HER2-positive advanced or metastatic breast cancer, yielding superior progression-free survival and response durability compared to the established taxane-trastuzumab-pertuzumab regimen. The safety profile is manageable but includes a notable risk of interstitial lung disease, requiring proactive management.
This trial advances the treatment paradigm, potentially improving long-term outcomes for this patient population. Further follow-up and head-to-head comparisons will refine optimal sequencing and combination strategies in HER2-directed therapies.
Funding and ClinicalTrials.gov
The DESTINY-Breast09 trial was funded by AstraZeneca and Daiichi Sankyo. ClinicalTrials.gov identifier: NCT04784715.
References
Tolaney SM, Jiang Z, Zhang Q, Barroso-Sousa R, Park YH, Rimawi MF, Saura C, Schneeweiss A, Toi M, Chae YS, Kemal Y, Chaudhari M, Şendur MAN, Yamashita T, Casalnuovo M, Danso MA, Liu J, Shetty J, Herbolsheimer P, Loibl S; DESTINY-Breast09 Trial Investigators. Trastuzumab Deruxtecan plus Pertuzumab for HER2-Positive Metastatic Breast Cancer. N Engl J Med. 2025 Oct 29. doi: 10.1056/NEJMoa2508668. Epub ahead of print. PMID: 41160818.
