Trastuzumab deruxtecan (T-DXd, DS-8201) is FDA-approved (Aug 2022) for unresectable or me...
Deterministic view of the source YAML entity. Clinical authority remains with the cited source IDs and reviewer sign-off state.
| ID | BMA-HER2-LOW-BREAST |
|---|---|
| Type | Actionability |
| Status | reviewed 2026-05-03 | pending_clinical_signoff | actionability review required |
| Diseases | DIS-BREAST |
| Sources | SRC-DESTINY-BREAST04-MODI-2022 SRC-ESMO-BREAST-METASTATIC-2024 SRC-NCCN-BREAST-2025 |
Actionability Facts
| Biomarker | BIO-HER2-LOW |
|---|---|
| Variant | IHC 1+ OR IHC 2+/ISH-negative (HER2-low by ASCO/CAP 2023 criteria) |
| Disease | DIS-BREAST |
| ESCAT tier | IA |
| Recommended combinations | trastuzumab deruxtecan (T-DXd) 5.4 mg/kg IV q3w monotherapy (post-chemotherapy; DESTINY-Breast04), trastuzumab deruxtecan (T-DXd) 5.4 mg/kg IV q3w monotherapy (post-endocrine HR+ disease; DESTINY-Breast06) |
| Contraindicated monotherapy | trastuzumab or pertuzumab (no anti-HER2 activity at IHC 1+/2+ ISH- level for these agents), T-DM1 (ado-trastuzumab emtansine) — approved for HER2+ (IHC 3+ or ISH+) only, not HER2-low |
| Evidence summary | Trastuzumab deruxtecan (T-DXd, DS-8201) is FDA-approved (Aug 2022) for unresectable or metastatic HER2-low (IHC 1+ or 2+/ISH-) breast cancer following prior chemotherapy. DESTINY-Breast04 (Modi et al. NEJM 2022): HR+/HER2-low — mPFS 10.1 vs 5.4 mo (HR 0.49, p<0.001); mOS 23.9 vs 17.5 mo (HR 0.64, p=0.003). HR-/HER2-low (TNBC subgroup) — mOS 18.2 vs 8.3 mo. DESTINY-Breast06 (Curigliano et al. NEJM 2024) extended indication to HER2-low and HER2-ultralow (IHC 0 with incomplete staining) HR+/HER2- endocrine-pretreated patients — mPFS 13.2 vs 8.1 mo (HR 0.62, p<0.001). T-DXd dose: 5.4 mg/kg IV q3w. Key safety: interstitial lung disease (ILD) / pneumonitis ~12% (grade ≥3 ~3%) — mandatory baseline CT and monitoring per NCCN/ESMO. HER2-low reclassification affects ~60% of previously HER2-negative metastatic breast cancer patients — large population impact. |
Notes
ESCAT IA. HER2-low reclassification (IHC 1+ or 2+/ISH-) is now clinically actionable — a paradigm shift from binary HER2+/- to a three-tier classification (HER2-positive / HER2-low / HER2-zero). Reflex HER2 IHC with careful 1+ vs 0 distinction now required on all metastatic breast specimens per NCCN/ESMO. ILD management: baseline CT chest, monitoring at each cycle, dose-reduction/hold/discontinue algorithm per NCCN. DESTINY-Breast06 further extended benefit to HER2-ultralow (IHC 0 with incomplete/faint staining) — this specific subgroup requires separate BIO entity (BIO-HER2-ULTRALOW) when reclassification is confirmed by pathology.
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