In the DESTINY‑11 trial for high‑risk HER2 (human epidermal growth factor receptor 2)‑positive early‑stage breast cancer (tumor ≥ cT3 cN0 or any cT0‑4 cN1‑3), what neoadjuvant regimen (trastuzumab deruxtecan (Enhertu) followed by trastuzumab, pertuzumab, paclitaxel (THP)) should be used instead of dose‑dense doxorubicin plus cyclophosphamide (ddAC) followed by THP?

DESTINY-Breast11: Trastuzumab Deruxtecan Followed by THP as New Neoadjuvant Standard

For high-risk HER2-positive early breast cancer (≥cT3cN0 or cT0-4cN1-3), trastuzumab deruxtecan (T-DXd) for 4 cycles followed by paclitaxel, trastuzumab, and pertuzumab (THP) for 4 cycles should replace dose-dense doxorubicin/cyclophosphamide (ddAC) followed by THP as the preferred neoadjuvant regimen. This recommendation is based on the DESTINY-Breast11 trial demonstrating superior pathological complete response (pCR) rates with significantly improved safety compared to the anthracycline-containing standard 1.

Evidence from DESTINY-Breast11

The phase III DESTINY-Breast11 trial enrolled 927 patients with high-risk HER2-positive early breast cancer across 147 sites in 18 countries. The T-DXd-THP arm achieved a pCR rate of 67.3% compared to 56.3% with ddAC-THP, representing an absolute difference of 11.2% (95% CI: 4.0-18.3%, P=0.003) 1.

Key Efficacy Findings:

• Hormone receptor-positive subgroup: pCR 61.4% (T-DXd-THP) vs 52.3% (ddAC-THP); difference 9.1%
• Hormone receptor-negative subgroup: pCR 83.1% (T-DXd-THP) vs 67.1% (ddAC-THP); difference 16.1%
• Event-free survival: Hazard ratio 0.56 (95% CI: 0.26-1.17) favoring T-DXd-THP, though with early maturity (4.5%)

The benefit was consistent across both HR-positive and HR-negative disease, with particularly impressive results in the HR-negative subset 1.

Superior Safety Profile

The T-DXd-THP regimen demonstrated substantially lower toxicity compared to anthracycline-based therapy:

• Grade ≥3 adverse events: 37.5% (T-DXd-THP) vs 55.8% (ddAC-THP)
• Serious adverse events: 10.6% (T-DXd-THP) vs 20.2% (ddAC-THP)
• Left ventricular dysfunction (all grades): 1.3% (T-DXd-THP) vs 6.1% (ddAC-THP)

Importantly, adjudicated drug-related interstitial lung disease/pneumonitis rates were low and similar across arms (4.4% for T-DXd-THP vs 5.1% for ddAC-THP), with most cases being low-grade and manageable 1.

Regulatory and Clinical Context

The FDA label for trastuzumab deruxtecan (Enhertu) supports its use in HER2-positive breast cancer, with established safety monitoring protocols for ILD/pneumonitis and cardiac function 2. The pertuzumab label confirms its role in neoadjuvant therapy for HER2-positive early breast cancer when tumor is >2 cm or node-positive 3.

Current NCCN guidelines (2024) list AC followed by paclitaxel plus trastuzumab ± pertuzumab as a preferred regimen for HER2-positive disease 4. However, these guidelines predate DESTINY-Breast11 results. The 2024 ESMO guidelines recommend neoadjuvant chemotherapy with dual HER2 blockade (trastuzumab and pertuzumab) for clinical stage II-III HER2-positive breast cancer 5.

Treatment Algorithm

For patients with high-risk HER2-positive early breast cancer:

1. Confirm HER2-positive status using FDA-approved testing (IHC or ISH) in CAP-accredited laboratories 6

2. Assess cardiac function with baseline LVEF measurement before initiating therapy 4, 3

3. Administer neoadjuvant regimen:

   • T-DXd 5.4 mg/kg IV every 3 weeks × 4 cycles
   • Followed by paclitaxel + trastuzumab + pertuzumab every 3 weeks × 4 cycles

4. Monitor during treatment:

   • LVEF assessment every 3 months during HER2-targeted therapy 4
   • Clinical monitoring for ILD/pneumonitis symptoms (dyspnea, cough, fever) 2
   • Hold T-DXd for Grade 2+ ILD until resolution to Grade 0-1 2

5. Post-neoadjuvant management:

   • If pCR achieved: Complete 1 year total of trastuzumab ± pertuzumab 7, 5
   • If residual invasive disease: Consider T-DM1 for 14 cycles 7, 5

Critical Caveats and Considerations

Cardiac monitoring is essential given the sequential use of multiple HER2-targeted agents. While T-DXd-THP showed lower cardiac toxicity than ddAC-THP, baseline cardiac assessment and serial monitoring remain mandatory 4, 3.

ILD/pneumonitis requires vigilance despite low rates in DESTINY-Breast11. Educate patients about respiratory symptoms and maintain a low threshold for imaging evaluation. Most cases are manageable with dose interruption and corticosteroids, but early detection is crucial 2, 1.

The T-DXd monotherapy arm (8 cycles) in DESTINY-Breast11 was closed early due to inferior pCR rates (43.0%), confirming that T-DXd alone is insufficient for high-risk disease 1. The combination with THP is necessary to achieve optimal outcomes.

For lower-risk disease (cT1a-b cN0), upfront surgery followed by adjuvant paclitaxel plus trastuzumab for 12 weeks remains appropriate, with consideration of adding pertuzumab if pathologically node-positive 7, 8.

Advantages Over Anthracycline-Based Therapy

The T-DXd-THP regimen offers multiple advantages:

• Avoids anthracycline-related toxicities: No risk of acute cardiotoxicity, febrile neutropenia, or secondary leukemia associated with doxorubicin
• Superior efficacy: Higher pCR rates translate to improved long-term outcomes, as pCR is a validated surrogate for event-free and overall survival 7
• Better tolerability: Lower rates of serious adverse events facilitate treatment completion
• Reduced cardiac risk: Particularly important given the need for extended HER2-targeted therapy

The TRAIN-2 trial previously demonstrated that anthracycline-free regimens (carboplatin-based) with dual HER2 blockade achieved similar pCR rates to anthracycline-containing regimens but with better safety 4. DESTINY-Breast11 extends this concept by showing that T-DXd-based therapy surpasses both approaches.

This represents a paradigm shift in neoadjuvant therapy for high-risk HER2-positive breast cancer, prioritizing both efficacy and safety through elimination of anthracyclines while incorporating the most potent HER2-targeted agent available.