ADCs Just Redefined Breast Cancer Care: What Enhertu, Dato-DXd, HER3-DXd, and BioNTech’s Newcomer Mean Right Now

• Enhertu expanded (Jan 27, 2025): first HER2-directed option for HR+ metastatic breast cancer with HER2-low or HER2-ultralow expression after endocrine therapy; based on DESTINY-Breast06. U.S. Food and Drug Administration, AstraZeneca
• Dato-DXd approved (Jan 17, 2025) for HR+ / HER2-negative metastatic breast cancer after prior endocrine therapy and chemotherapy; TROPION-Breast01. U.S. Food and Drug Administration AstraZeneca
• HER3-DXd stumble: patritumab deruxtecan’s US BLA withdrawn after Phase 3 OS disappointment in EGFR-mutant NSCLC; filing originally sought accelerated approval off Phase 2 data. OncLive, Applied Clinical Trials Online, Targeted Oncology
• A new HER2 ADC rising: BioNTech/DualityBio’s trastuzumab pamirtecan (BNT323) beat Kadcyla on PFS in a China Phase 3 trial of previously treated HER2-positive breast cancer—BioNTech’s first late-stage oncology win. ReutersInside Precision Medicine

Why this matters: the ADC wave, explained

Antibody–drug conjugates (ADCs) pair a targeting antibody (e.g., anti-HER2 or anti-TROP2) with a high-potency payload via a linker. They are shifting treatment from “chemotherapy for all” to precision chemo delivery, improving response rates and durability while introducing class-specific toxicities (notably interstitial lung disease with topoisomerase-I payloads and stomatitis with TROP2 agents).

The 2025 decisions above broaden who qualifies (new HER2-ultralow category) and when ADCs appear (post-endocrine therapy for HR+ disease, earlier than before). They also show the market maturing: wins for some assets and course-corrections for others.

What changed with HER2 testing (and why “ultralow” is a big deal)

• HER2-low = IHC 1+ or IHC 2+/ISH–; HER2-ultralow = IHC 0 with faint membrane staining—now recognized in the FDA label. This creates a much larger HR+ population eligible for HER2-directed ADCs after endocrine therapy. U.S. Food and Drug Administration
• Practical takeaway: ask pathology to report IHC 0 vs 0 (ultralow) and ensure labs use validated, FDA-cleared assays; eligibility hinges on these nuances.

The big four: what the data actually say

1) Trastuzumab deruxtecan (Enhertu, T-DXd)

• Indication (US, Jan 2025): unresectable/metastatic HR+ breast cancer that is HER2-low or HER2-ultralow and has progressed on ≥1 endocrine therapy. U.S. Food and Drug Administration
• DESTINY-Breast06 results (regulatory dataset):
  • PFS: 13.2 vs 8.1 months vs chemo (HR 0.64; 95% CI 0.54–0.76; p<0.0001). AstraZeneca
• Clinical implications: moves T-DXd earlier in HR+ disease, before traditional chemo in many pathways.
• Safety watch-outs: interstitial lung disease/pneumonitis (requires early recognition, steroid management), cytopenias, nausea; follow label monitoring guidance. AstraZeneca US

Example patient
A 56-year-old with de novo HR+ MBC, initial response to aromatase inhibitor + CDK4/6 inhibitor, now progressed; IHC returns HER2-ultralow. Under 2025 label, she becomes eligible for Enhertu before moving to capecitabine or taxane—potentially adding ~5 months median PFS over chemo in trial conditions. AstraZeneca

2) Datopotamab deruxtecan (Dato-DXd; brand Datroway in US labeling)

• Indication (US, Jan 2025): unresectable/metastatic HR+ / HER2-negative breast cancer after prior endocrine-based therapy and chemotherapy in the metastatic setting. U.S. Food and Drug Administration, AstraZeneca US
• TROPION-Breast01 highlights:
  • Risk reduction in progression/death ~37% vs investigator’s-choice chemo (docetaxel/paclitaxel/eribulin) → implies HR ≈0.63. AstraZeneca US
• Clinical implications: establishes TROP2-targeting ADCs as a post-chemo standard for HR+ disease, complementing T-DXd’s earlier-line role.
• Safety watch-outs: stomatitis/oral mucositis is common; proactive oral care and dose modifications matter. ILD risk exists but appears lower than with HER2-DXd in trial reporting. (See FDA label and press release safety sections.) U.S. Food and Drug Administration

Example patient
A 62-year-old with HR+ / HER2-negative MBC progressed on AI+CDK4/6 and later on weekly paclitaxel. She is now a clear Dato-DXd candidate, where data suggest a meaningful PFS advantage and manageable stomatitis with prophylaxis. AstraZeneca US

3) Patritumab deruxtecan (HER3-DXd) — a reality check

• What happened: Daiichi Sankyo/Merck withdrew the US BLA (May 2025) after the confirmatory HERTHENA-Lung02 Phase 3 missed OS goals, undermining the accelerated-approval path that leaned on HERTHENA-Lung01 Phase 2 data. Applied Clinical Trials Online, OncLive, Targeted Oncology
• Clinical implications: No US approval for EGFR-mutant, previously treated NSCLC. ADC momentum doesn’t guarantee OS wins; expect more selective development and better biomarker strategies for HER3.
• Lesson: not all ADC targets translate to survival benefit; regulators are pressing for robust OS evidence despite impressive response rates.

4) Trastuzumab pamirtecan (BNT323) — the new HER2 contender

• News (Sept 2025): In a China Phase 3 trial of previously treated HER2-positive unresectable/metastatic breast cancer, BNT323 beat Kadcyla (T-DM1) on PFS (full numbers pending publication). BioNTech/DualityBio plan China filings and global program expansion, including HER2-low cohorts. Reuters, Inside Precision Medicine
• Why it’s notable: represents BioNTech’s first late-stage oncology win, signaling next-gen HER2 ADC competition beyond Enhertu/T-DM1—potentially different linker/payload dynamics aiming for higher potency with controllable safety.

Example scenario
As BNT323 data mature globally, regions without broad Enhertu access—or patients progressing after Kadcyla in countries where it remains a common second-line—may gain another HER2-directed ADC choice, subject to local approvals and head-to-head comparative data. Reuters

How clinicians can operationalize this now

1. Re-tool pathology workflows

• Request granular HER2 IHC reporting (explicitly note ultralow) and ensure assay concordance with FDA-cleared tests to avoid false negatives that could deny patients ADC access. U.S. Food and Drug Administration

2. Sequence thoughtfully in HR+ disease

• After endocrine therapy → consider Enhertu for HER2-low/ultralow before conventional chemo.
• After chemo exposure → for HR+ / HER2-negative, pivot to Dato-DXd per TROPION-Breast01. Real-world factors (ILD risk, mucositis, prior lung disease, oral care access) may guide which ADC first if a patient qualifies for both at different times. AstraZeneca

3. Safety infrastructure

• Build ILD monitoring pathways (baseline imaging, symptom education, swift steroids, dose holds) for DXd-class agents. Set stomatitis prevention kits (oral rinses, dental review) for Dato-DXd starts. AstraZeneca US, U.S. Food and Drug Administration

4. Trials and next-ups

• For EGFR-mutant NSCLC, reset expectations post-HER3-DXd and look to alternative ADCs or targeted/IO combinations in trials.
• Watch for global readouts/filings of BNT323 beyond China and head-to-head data that clarify positioning vs Enhertu/T-DM1. Reuters

A quick look beyond breast: ADC momentum keeps building

While this article centers on HR+ and HER2-positive breast cancer, the broader ADC pipeline continues to expand:

• Ifinatamab deruxtecan (I-DXd) in extensive-stage SCLC hit 48% ORR in a registrational Phase 2 (IDeate-Lung01); companies have started talks with regulators—an example of ADCs reaching historically tough tumors. DSI, Fierce Biotech, OncLive

Source list (primary/official where possible)

• FDA approvals:
  • Enhertu (fam-trastuzumab deruxtecan-nxki) for HR+ HER2-low/ultralow MBC (Jan 27, 2025) + label language and test definitions. U.S. Food and Drug Administration
  • Datopotamab deruxtecan (Datroway) for HR+ / HER2-negative MBC (Jan 17, 2025). U.S. Food and Drug Administration
• Company/press releases with efficacy details:
  • AstraZeneca/Daiichi Sankyo – Enhertu DESTINY-Breast06 PFS (HR 0.64; 13.2 vs 8.1 mo). AstraZeneca
  • AstraZeneca (US) – Datroway TROPION-Breast01 (37% risk reduction). AstraZeneca US
• Regulatory setback:
  • Patritumab deruxtecan BLA withdrawal (HER3-DXd) — Applied Clinical Trials; OncLive; Targeted Oncology. Applied Clinical Trials Online, OncLive, Targeted Oncology
• New HER2 ADC:
  • BioNTech/DualityBio BNT323 (trastuzumab pamirtecan) Phase 3 win vs Kadcyla — Reuters; Inside Precision Medicine. Reuters, Inside Precision Medicine
• ADC in SCLC (signal for the broader wave):
  • Ifinatamab deruxtecan Phase 2 ORR 48.2%, regulatory discussions underway — Daiichi Sankyo press note; Fierce Biotech; OncLive. DSI, Fierce Biotech, OncLive

Bottom line

• Enhertu’s expansion plus Dato-DXd’s approval reshaped the HR+ metastatic landscape in 2025—earlier ADC use, more patients eligible, and better median PFS than chemo in pivotal trials. AstraZeneca
• HER3-DXd’s withdrawal is a reminder that ADC success needs OS and the right biology. Applied Clinical Trials Online
• BNT323 signals next-gen HER2 competition—expect pricing, access, and sequencing debates as data globalize. Reuters