Background
Phase III, open-label RCT. ~1600 patients with HER2+ early breast cancer who had residual invasive disease after neoadjuvant HER2-directed therapy (the same post-NACT residual-disease population as KATHERINE). Designed as a head-to-head comparison of T-DXd (next-generation ADC) vs T-DM1 (established standard) to directly challenge the KATHERINE standard of care.
Interventions and follow up
Arm A: T-DXd (trastuzumab deruxtecan) 5.4mg/kg IV q21d × 14 cycle
Arm B: T-DM1 (trastuzumab emtansine) 3.6mg/kg IV q21d × 14 cycle
Primary endpoint: Invasive disease-free survival (IDFS)
mFollow up: ~36 months (primary analysis)
Arm B: T-DM1 (trastuzumab emtansine) 3.6mg/kg IV q21d × 14 cycle
Primary endpoint: Invasive disease-free survival (IDFS)
mFollow up: ~36 months (primary analysis)
Results
IDFS: HR 0.64, 95% CI 0.51–0.80, P<.001
3-yr IDFS rate: 89.8% (T-DXd) vs 84.9% (T-DM1)
OS: Immature at primary analysis
3-yr IDFS rate: 89.8% (T-DXd) vs 84.9% (T-DM1)
OS: Immature at primary analysis
Adverse events
Pulmonary: ILD any grade 10.4% (T-DXd) vs 0.6% (T-DM1); grade ≥3 1.0% (T-DXd)
GI: grade ≥3 nausea 4.5% vs 2.0%
Hematologic: grade ≥3 thrombocytopenia 1.8% (T-DXd) vs 6.5% (T-DM1)
Neurologic: grade ≥3 peripheral neuropathy 0.4% (T-DXd) vs 2.2% (T-DM1)
Other: discontinuation 16.5% (T-DXd) vs 18.4% (T-DM1)
GI: grade ≥3 nausea 4.5% vs 2.0%
Hematologic: grade ≥3 thrombocytopenia 1.8% (T-DXd) vs 6.5% (T-DM1)
Neurologic: grade ≥3 peripheral neuropathy 0.4% (T-DXd) vs 2.2% (T-DM1)
Other: discontinuation 16.5% (T-DXd) vs 18.4% (T-DM1)
Conclusions
T-DXd significantly improved IDFS compared to T-DM1 in HER2+ early BC with residual disease after NACT, with a 36% relative risk reduction and ~5% absolute benefit at 3 years. T-DXd has replaced T-DM1 as the new standard of care in this post-NACT residual-disease setting.
Key Limitations
Key Limitations: ILD rate of 10.4% with T-DXd (vs 0.6% with T-DM1) is a critical safety concern requiring systematic pulmonary monitoring — a meaningful toxicity shift from T-DM1's thrombocytopenia/neuropathy profile. OS data remain immature. Direct comparison with other strategies in HER2+ residual disease (e.g., pertuzumab continuation) not performed. Patients who received T-DM1 per KATHERINE after prior trastuzumab-only NACT represent a distinct population from those receiving T-DXd after dual HER2 blockade (pertuzumab+trastuzumab) NACT — cross-trial comparisons are limited.
Clinical Context
DESTINY-Breast05 established T-DXd as the new adjuvant standard over T-DM1 in HER2+ early BC with residual disease (FDA approved 2024). ESMO-MCBS score: pending OS data. This result, combined with DESTINY-Breast03 in metastatic HER2+, completes T-DXd's dominance across HER2+ settings from early to metastatic disease. ILD monitoring protocols developed from metastatic DB trials apply in this adjuvant context.
References
References: Hurvitz SA et al, NEJM 2024