Trastuzumab Deruxtecan (DS-8201a) for the Treatment of Recurrent or Refractory Osteosarcoma, Wilms Tumor, and Desmoplastic Small Round Cell Tumor

1. Is the biology right?

• Somatic driver evidence: yes · TOP1 in osteosarcoma

  Rule: Open Targets has somatic-mutation evidence for the target in this cancer. Source: Open Targets: TOP1 in osteosarcoma, 2026-11-11

  Published context: 2.3× relative success for targets with somatic (IntOGen) support in oncology (Minikel et al., Nature 2024, drug programs to 2023). A ratio between groups, not a probability for this program; mostly phase 2 to 3.
• Human genetic evidence: yes · TOP1: somatic

  Rule: Any germline or somatic human genetic evidence for the target in this cancer, counted apart from animal-model and literature evidence. Source: Open Targets: TOP1 in osteosarcoma, 2026-11-11

  Published context: 2.6× relative probability of success, phase 1 to launch, with human genetic support (Minikel et al., Nature 2024, drug programs to 2023). All therapy areas, mostly germline evidence; not a probability for this program.
• Pediatric target: yes · ERBB2 on the FDA list

  Rule: Target is on FDA's Pediatric Molecular Target List (relevant targets); membership alone neither requires nor waives a study. Source: FDA Pediatric Molecular Target List (Listed as February 2026 on the FDA Pediatric Oncology page; the file served is 9.7.22_the_relevant_molecular_target_list.xlsx, whose Summary of Changes sheet is headed 'SEPTEMBER 2022 UPDATE' (footnote date 2022-09-01)), 2026-11-11
• Haematologic cancer: no · Solid tumour

  Rule: From the indication, or the registry conditions when no indication matches. Source: ClinicalTrials.gov NCT04616560, 2026-11-11

  Published context: Likelihood of approval from phase 1: 7.5% haematologic vs 4.6% solid (BIO / Informa / QLS 2021, 2011–2020). Population-level, not a prediction.

• ERBB2 (via Trastuzumab Deruxtecan): Evidence types in osteosarcoma: literature, clinical; literature listed separately from human genetics. Datasources: europepmc, clinical_precedence. · Open Targets: ERBB2 in osteosarcoma
• TOP1 (via Trastuzumab Deruxtecan): Evidence types in osteosarcoma: literature, somatic_mutation, clinical; literature listed separately from human genetics. Datasources: clinical_precedence, cancer_gene_census, europepmc. · Open Targets: TOP1 in osteosarcoma

• Not loaded on this app yet: Normal-tissue expression in vital organs. Source: Human Protein Atlas (ticket 36).
• Not loaded on this app yet: Pan-essential in cell lines. Source: DepMap (ticket 36).
• Not loaded on this app yet: Approved drug on this target. Source: Drugs@FDA (ticket 30).

2. Can the result be trusted?

• Randomised: no · Single group

  Rule: Registry allocation field. Source: ClinicalTrials.gov NCT04616560, 2026-11-11
• Small denominator: no · 55 planned; each patient moves a rate by 100 ÷ 55 = 1.8 points

  Rule: Enrolment under 30; the arithmetic is shown, not a benchmark. Source: ClinicalTrials.gov NCT04616560, 2026-11-11
• Primary endpoint is overall survival: no · Maximum tolerated dose and/or recommended phase 2 dose of DS-8201a in children at least 2 to less than 12 years old w…; Incidence of adverse events (AEs) in children at least 2 to less than 12 years old with recurrent or refractory WT or…; Time to progression

  Rule: A registered primary outcome measure names overall survival. Source: ClinicalTrials.gov NCT04616560, 2026-11-11

  Published context: Non-OS primary endpoint: odds ratio 2.79 for a positive phase 3 (Otsuka 2021, 400 phase 3 oncology trials, to 2020). Shown with the next figure: a surrogate is easier to hit, and often a weak guide to survival.

  Published context: 52% of surrogate-to-OS correlations are low (Prasad 2015, published to 2014). Shown with the figure above.
• Results overdue: no · Primary completion expected 2027-12-31; not yet due

  Rule: Primary completion (actual) more than 12 months ago and no results posted to the registry. Source: ClinicalTrials.gov NCT04616560, 2026-11-11

• Not loaded on this app yet: Treated and evaluable counts, assessor, confirmed response, follow-up and data cutoff. Source: Readout extraction (ticket 32).
• Not loaded on this app yet: Primary endpoint changed between registry versions. Source: Registry versions in the store (ticket 32).

3. What must it beat?

• Not loaded on this app yet: Control-arm result and approved therapies for the same segment, with label links. Source: Drugs@FDA, FDA labels and readouts (tickets 30, 32).

4. Too crowded, or too late?

• Stopped on this target: 192 terminated, withdrawn or suspended trials of drugs against ERBB2; 21 give no reason. Reasons are quoted as the registry gives them on the target page. · ERBB2: what already stopped

• Not loaded on this app yet: Programs on the target by phase and months behind the leader. Source: Programs and Drugs@FDA (ticket 33).

5. Can it be approved, and stay approved?

• Single-country: yes · All 32 sites in United States

  Rule: All listed sites are in one country; the share of US sites is shown. Source: ClinicalTrials.gov NCT04616560, 2026-11-11
• EU paediatric investigation plan: yes · EMEA-002978-PIP02-24 (trastuzumab deruxtecan, Treatment of all conditions in the category of malignant neoplasms (except haematopoietic and lymphoid tissue neoplasms)): P: decision agreeing on a investigation plan, with or without partial waiver(s) and or deferral(s), 5 Dec 2024; EMEA-002978-PIP01-21 (trastuzumab deruxtecan, Treatment of lung cancer): W: decision granting a waiver in all age groups for all conditions or indications, 8 Jul 2021; EMEA-002976-PIP01-21 (trastuzumab deruxtecan, Treatment of lung cancer): W: decision granting a waiver in all age groups for all conditions or indications, 9 Jul 2021

  Rule: An EMA PIP decision (agreement, modification or waiver) lists the drug as its active substance, exact name. Source: EMA data download (dated snapshot), 2026-11-11
• EU orphan designation: no · No EU orphan designation names Trastuzumab Deruxtecan

  Rule: An EU orphan designation lists the drug as its active substance (exact name) or belongs to a medicine that does; withdrawn and expired designations are listed with their status. Source: EMA data download (dated snapshot), 2026-11-11
• Authorised in the EU: yes · Enhertu: authorised since 18 Jan 2021, conditional

  Rule: An EMA medicine record lists the drug as its active substance or INN, exact name; national-only authorisations are not in this file. Source: EMA EPAR Enhertu, 2026-11-11
• FDA orphan designation: not published · FDA's orphan designation database turns away automated requests, so this app does not read it; search it by hand at the link

  Rule: Would be: an FDA orphan designation names the drug. Source: FDA orphan designations search
• FDA pediatric oncology approval: no · FDA's table lists no pediatric approval of Trastuzumab Deruxtecan

  Rule: FDA's Pediatric Oncology Drug Approvals table names the drug. Source: FDA Pediatric Oncology Drug Approvals (content current as of 2026-03-03), 2026-11-11
• Registered studies open to children: yes · 2 interventional studies of Trastuzumab Deruxtecan include patients under 18; 2 are recruiting, not yet recruiting or active

  Rule: The registry's age group includes Child (birth to 17 years), which also counts studies that set no minimum age. Source: ClinicalTrials.gov search, 2026-11-11

• Caveat: Site counts are not patients per country, and trials registered only outside ClinicalTrials.gov are not covered. Where the sites are is a fact about the record, not a judgement of its quality.
• Rare pediatric disease voucher: FDA, content current as of 29 Apr 2026: “As of February 3, 2026, enactment of the Consolidated Appropriations Act, 2026, the rare pediatric disease PRV program will sunset after September 30, 2029. FDA may not award any PRVs under this program after September 30, 2029.” Voucher sale prices are not shown here; they appear only as company-reported news. · FDA: Rare Pediatric Disease Designation and Priority Review Voucher Programs

• Not loaded on this app yet: Precedent approvals for target, modality and endpoint; accelerated-approval status. Source: Drugs@FDA and FDA accelerated-approval tables (ticket 30).

6. Can the sponsor finish?

• Sponsor: National Cancer Institute (NCI) (academic or other) · ClinicalTrials.gov NCT04616560
• principal investigator: Damon R Reed, Pediatric Early Phase Clinical Trial Network · Person page

• Not loaded on this app yet: Filed cash, quarterly spend and the runway arithmetic. Source: SEC XBRL company facts (ticket 37).
• Not loaded on this app yet: Sponsor's completed vs stopped oncology trials and results-reporting record. Source: Registry, by company (ticket 37).

What public data cannot tell you

Public records cannot show: sales forecasts; a probability of success for this asset; full deal terms and net prices; FDA designations and action dates before approval (shown only as company-reported); clinical holds unless the company disclosed them; manufacturing; patents on unapproved drugs; whether preclinical findings have been replicated.