DESTINY-Breast08: Trastuzumab Deruxtecan for First-Line Treatment of HER2-Low Breast Cancer
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Targeting the cell’s “dynamic response”, not its “static code”: T-DXd’s synergistic dance with chemotherapy, AKT inhibitors and endocrine therapy.
With the DESTINY-Breast04 and 06 studies, trastuzumab deruxtecan (T-DXd) established a new standard in the HER2-low (IHC 1+ or IHC 2+/ISH-) population. Scientific curiosity, however, did not stop there. Preclinical data show that chemotherapy and endocrine therapy can increase HER2 protein expression on the cell surface (upregulation), thereby creating a more “precise” target for T-DXd. The DESTINY-Breast08 study, by using T-DXd not only alone but also with molecular partners that disrupt resistance pathways (AKT inhibitors, etc.) and starting from the first line , provides a translational roadmap for making treatment responses durable.
Study design: a two-phase, five-module architecture
DESTINY-Breast08 is an open-label, multicentre, modular phase Ib study. Its “innovative” aspect is testing T-DXd not only as salvage therapy but from the very beginning of the metastatic stage.
| Study Phase | Target Population | Clinical Focus |
|---|---|---|
| Dose Finding (Part 1) | 2nd Line and Beyond (Heavily Pretreated) | Determining the safe dose (RP2D) and tolerability. |
| Dose Expansion (Part 2) | First (1L) and Second (2L) Line | Measuring preliminary antitumour activity and success by treatment line. |
Study participants were assigned to the following modules according to their hormone receptor (HR) status and genetic profiles:
“Cross-cytotoxicity” was targeted by exploiting chemotherapy’s ability to trigger HER2 upregulation.
A translational arm aiming to enhance ADC efficacy by shutting down the PI3K/AKT pathway in resistant cases.
A strategy of blocking HER2/ER “cross-talk” from both sides with anastrozole or fulvestrant.
The durvalumab + paclitaxel arm was not continued after the dose-finding phase for strategic reasons.
Clinical findings: response rates in the 1st and 2nd lines
In the dose-expansion phase, T-DXd combinations showed striking response rates in the HER2-low mBC population, particularly in the “hormone-sensitive” subgroup.
Objective Response Rates in the Combination Arms (cORR)
Molecular Synergy: The Capivasertib Arm
In patients with a mutation in the PI3K/AKT pathway (PIK3CA, AKT1 or PTEN), the response rate rose to 76.9%, whereas it remained at 52.4% in the group without mutations. As part of our understanding of “precision medicine”, this finding proves the potential synergy between ADCs and targeted agents that overcome resistance.
Safety profile: ILD management and the cost of toxicity
Combination therapies bring a biological cost as well as efficacy. The toxicity profile observed in DESTINY-Breast08 is consistent with the individual profile of each component.
Interstitial Lung Disease (ILD) Analysis
Across all modules, the rate of drug-related ILD/pneumonia was 15.8% (16/101 patients). Although 93.8% of events were low grade (Grade 1-2), in the capecitabine arm one fatal (Grade 5) case was reported. Patients over 65, those with renal insufficiency and those who previously received thoracic radiation require the closest monitoring with these combinations.
Other common serious (Grade ≥3) adverse events were nausea and diarrhoea in the capivasertib arm (67.5%), and vomiting and hand-foot syndrome in the capecitabine arm (55.0%). These data prove how delicate the balance of “preserving quality of life” is when moving treatment to an earlier line.
DROZDOGAN Academy Commentary
DESTINY-Breast08 reminds us of oncology’s oldest truth: “A tumour is not a static target; it is a living, changing organism.” We applauded T-DXd’s success alone, but this study shows us how to make the target on the cell surface “more visible” through other treatments (upregulation) and how to precisely shut down resistance pathways.
The 71% response rate in the anastrozole arm, in particular, is a sign of how effective the dance between endocrine therapy and ADCs could be in the first line. Provided that side effects, especially pulmonary toxicity, are managed with “precise guidance”, T-DXd combinations will form the standard architecture of the personalised oncology of the future.
Academic Sources and Further Reading
- 1. Jhaveri K, et al. DESTINY-Breast08: A Phase Ib Study of T-DXd in Combination in HER2-Low Metastatic Breast Cancer. Clin Cancer Res. 2026;32(6):1046-1058.
- 2. Modi S, et al. Trastuzumab Deruxtecan in Previously Treated HER2-Low Metastatic Breast Cancer (DESTINY-Breast04). N Engl J Med. 2022.
- 3. Bardia A, et al. DESTINY-Breast06: T-DXd in HR+, HER2-low or HER2-ultralow mBC. Journal of Clinical Oncology. 2024.
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