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Patritumab deruxtecan for children with relapsed or refractory hepatoblastoma or rhabdomyosarcoma

LIGHTBEAM-U01 Substudy 01C: A Phase 1/2 Substudy to Evaluate the Safety and Efficacy of Patritumab Deruxtecan in Pediatric Participants With Relapsed or Refractory Solid Tumors

Phase1; Phase2 Interventional Merck Sharp & Dohme LLC · NCT06941272

This trial tests an antibody-drug conjugate called HER3-DXd (patritumab deruxtecan) to see if it is safe and can shrink relapsed or treatment-resistant hepatoblastoma or rhabdomyosarcoma in children.

Quick facts

PhasePhase1; Phase2
Study typeInterventional
Enrollment50 (estimated)
Ages1 Month to 17 Years
SexAll
SponsorMerck Sharp & Dohme LLC Industry-sponsored
Drugs / interventionspatritumab
Locations60 sites (Los Angeles, California and 59 other locations)
Trial IDNCT06941272 on ClinicalTrials.gov

What this trial studies

This phase 1/2 interventional trial gives HER3-DXd (patritumab deruxtecan), an antibody-drug conjugate that delivers chemotherapy to cells expressing the HER3 protein, to pediatric participants with relapsed or refractory hepatoblastoma or rhabdomyosarcoma. Part 1 is a safety lead-in to identify a tolerable dose and characterize pharmacokinetics, and Part 2 evaluates efficacy at the recommended phase 2 dose. Key outcomes include safety/tolerability, drug behavior in the body, and objective tumor response. The trial is sponsored by Merck with collaboration from Daiichi Sankyo and is conducted at multiple U.S. pediatric cancer centers.

Who should consider this trial

Good fit: Children with histologically confirmed hepatoblastoma or rhabdomyosarcoma that has relapsed or is refractory after at least one prior systemic treatment and who have no satisfactory alternative standard treatments may be eligible.

Not a fit: Patients whose tumors lack the HER3 target, who have effective standard therapies available, or who do not meet required recovery or organ function criteria are unlikely to receive benefit from this investigational drug.

Why it matters

Potential benefit: If successful, HER3-DXd could provide a new targeted treatment option that shrinks tumors and helps children whose cancers have returned or not responded to prior therapy.

How similar studies have performed: Early adult studies of patritumab deruxtecan have demonstrated activity in some HER3-expressing solid tumors, but its use in pediatric hepatoblastoma and rhabdomyosarcoma is novel and unproven.

Eligibility criteria

Show full inclusion / exclusion criteria 
The main inclusion criteria include but are not limited to the following:

* Has one of the following histologically confirmed advanced or metastatic solid tumors: Rhabdomyosarcoma (RMS), or Hepatoblastoma
* Has progressed after at least 1 prior systemic treatment for RMS or hepatoblastoma and who has no satisfactory alternative treatment option (ie, is ineligible for other standard treatment regimens)
* Participants who have adverse events (AEs) due to previous anticancer therapies must have recovered to Grade ≤1 or baseline. Participants with endocrine-related AEs who are adequately treated with hormone replacement or participants who have Grade ≤2 neuropathy are eligible. Participants with Grade ≤2 alopecia are also eligible
* Hepatitis B surface antigen (HBsAg) positive participants are eligible if they have received hepatitis B virus (HBV) antiviral therapy and have undetectable HBV viral load
* Participants with a history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable

The main exclusion criteria include but are not limited to the following:

* Has a history of (noninfectious) interstitial lung disease (ILD)/pneumonitis that required steroids or has current ILD/pneumonitis, and/or suspected ILD/pneumonitis that cannot be ruled out by standard diagnostic assessments
* Has clinically severe respiratory compromise resulting from intercurrent pulmonary illness
* Has a history of solid organ transplant
* Has a history of allogeneic stem cell transplant
* Has clinically significant corneal disease
* Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis/leptomeningeal disease; participants with previously treated brain metastases may participate provided they are radiologically stable (ie, without evidence of progression) for at least 4 weeks
* Has uncontrolled or significant cardiovascular disorder
* Has a history of clinically significant congenital cardiac syndrome
* Has a history of human immunodeficiency virus (HIV) infection
* Has a known additional malignancy that is progressing or has required active treatment within the past 1 year
* Has an active infection requiring systemic therapy
* Has concurrent active hepatitis B (HBsAg positive and/or detectable HBV deoxyribonucleic acid \[DNA\]) and HCV defined as anti-HCV antibody (Ab) positive and detectable HCV ribonucleic acid \[RNA\]) infection
* Has not adequately recovered from major surgery or have ongoing surgical complications

Where this trial is running

Los Angeles, California and 59 other locations

+10 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Malignant Neoplasm
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.