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NCT Number: NCT06941272

A Study of Patritumab Deruxtecan in Pediatric Participants With Relapsed or Refractory Solid Tumors (MK-9999-01C/LIGHTBEAM-U01)

Researchers are looking for new ways to treat children with hepatoblastoma or rhabdomyosarcoma (RMS) that has relapsed or is refractory:

* Hepatoblastoma is a common liver cancer in babies and very young children * RMS is a cancer that starts in muscle cells, often in a child's head and neck, bladder, arms, or legs * Relapsed means the cancer came back after treatment * Refractory means the cancer did not respond (get smaller or go away) to treatment

The study treatment HER3-DXd (also known as MK-1022 or patritumab deruxtecan) is an antibody-drug conjugate (ADC). An ADC attaches to a protein on cancer cells and delivers treatment to destroy those cells. The goals of this study are to learn:

* About the safety of HER3-DXd in children and if they tolerate it * What happens to HER3-DXd in children's bodies over time * If children who receive HER3-DXd have the cancer get smaller or go away

Recruiting

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Key information

Conditions

Malignant Neoplasm Neoplasms

Age range

1 month–17 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 1 / Phase 2

Primary location

Sydney Children's Hospital-Kids Cancer Centre ( Site 3997), Sydney, New South Wales, Australia

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About this study

This study will have 2 parts: a safety lead-in to demonstrate a tolerable safety profile and confirm a preliminary recommended phase 2 dose (RP2D) (Part 1) followed by an efficacy evaluation (Part 2)

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

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 interstitial lung disease (ILD)/pneumonitis irrespective of steroid use, or current ILD/pneumonitis, or suspected ILD/pneumonitis, or ILD that cannot be ruled out by imaging
  • 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

Treatment and study plan

Patritumab deruxtecan

Biological

IV Infusion

Other names: MK-1022, HER3-DXd, U3-1402

Primary outcomes

  1. Part 1: Percentage of Participants Who Experience Dose-limiting Toxicities (DLTs)

    Time frame: Cycle 1 (up to approximately 21 days); each cycle is 21 days

    A DLT is any of a prespecified list of adverse events (AEs) that occur during Cycle 1 (up to 21 days) if attributed to the study treatment and not attributed to any other clearly identifiable cause. The percentage of participants who experience DLTs will be reported. Each cycle is 21 days.

  2. Part 1: Percentage of Participants Who Experience an Adverse Event (AE)

    Time frame: Up to approximately 5 years

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who experience AEs will be reported.

  3. Part 1: Percentage of Participants Who Discontinue Study Treatment Due to an AE

    Time frame: Up to approximately 5 years

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who discontinue study treatment due to an AE will be reported.

  4. Part 1: Area Under the Curve (AUC) of total anti-HER3 antibody liquid chromatography-mass spectrometry (LC-MS) in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  5. Part 1: AUC of anti-HER3 antibody-conjugated DXd (anti-HER3-ac-DXd) in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  6. Part 1: AUC of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  7. Part 1: Maximum Concentration (Cmax) of anti-HER3 antibody LC-MS in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  8. Part 1: Cmax of anti-HER3-ac-DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  9. Part 1: Cmax of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  10. Part 1: Concentration Immediately Before the Next Dose is Administered (Ctrough) of anti-HER3 antibody LC-MS in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

  11. Part 1: Ctrough of anti-HER3-ac-DXd

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

  12. Part 1: Ctrough of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

  13. Part 1 and Part 2: Objective Response Rate (ORR)

    Time frame: Up to approximately 5 years

    ORR is defined as the percentage of participants with Complete Response (CR: disappearance of all target lesions) or Partial Response (PR: at least a 30% decrease in the sum of diameters of target lesions) per Response Evaluation Criteria In Solid Tumors Version 1.1 (RECIST 1.1). The percentage of participants who experience CR or PR as assessed by the investigator will be presented.

Secondary outcomes

  1. Part 2: Percentage of Participants Who Experience an AE

    Time frame: Up to approximately 5 years

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who experience AEs will be reported.

  2. Part 2: Percentage of Participants Who Discontinue Study Treatment Due to an AE

    Time frame: Up to approximately 5 years

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who discontinue study treatment due to an AE will be reported.

  3. Part 1 and Part 2: Disease Control Rate (DCR)

    Time frame: Up to approximately 5 years

    DCR is defined, per RECIST 1.1, as the percentage of participants who have a CR (disappearance of all target lesions) or PR (at least a 30% decrease in the sum of diameters of target lesions) or Stable Disease (SD). SD is defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for progressive disease (PD: at least a 20% increase in the sum of diameters of target lesions and an absolute increase of at least 5 mm). Note: The appearance of one or more new lesions is also considered PD. The time from the first dose until the date of SD must be greater than or equal to 6 weeks. The DCR as assessed by the investigator will be presented.

  4. Part 1 and Part 2: Time to Response (TTR)

    Time frame: Up to approximately 5 years

    For participants who demonstrate a confirmed CR (disappearance of all target lesions) or PR (at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1, TTR is defined as the time from the first dose to the first documented evidence of a CR or PR. The TTR as assessed by the investigator will be presented.

  5. Part 1 and Part 2: Duration of Response (DOR)

    Time frame: Up to approximately 5 years

    For participants who demonstrate a confirmed CR (disappearance of all target lesions) or PR (at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1, DOR is defined as the time from first documented evidence of CR or PR until PD or death. PD is defined as at least a 20% increase in the sum of diameters of target lesions and an absolute increase of at least 5 mm. Note: The appearance of one or more new lesions is also considered PD. DOR as assessed by the investigator will be presented.

  6. Part 1 and Part 2: Progression-free Survival (PFS)

    Time frame: Up to approximately 5 years

    PFS is defined as the time from randomization to the first documented PD or death due to any cause, whichever occurs first as assessed by RECIST 1.1. PD is defined as at least a 20% increase in the sum of diameters of target lesions and an absolute increase of at least 5 mm. Note: The appearance of one or more new lesions is also considered PD. PFS as assessed by the investigator will be presented.

  7. Part 1 and Part 2: Overall Survival (OS)

    Time frame: Up to approximately 5 years

    OS is defined as time from first dose of study treatment to death due to any cause.

  8. Part 2: AUC of total anti-HER3 antibody LC-MS in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  9. Part 2: AUC of anti-HER3-ac-DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  10. Part 2: AUC of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of AUC.

  11. Part 2: Cmax of anti-HER3 antibody LC-MS in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  12. Part 2: Cmax of anti-HER3-ac-DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  13. Part 2: Cmax of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Cmax.

  14. Part 2: Ctrough of anti-HER3 antibody LC-MS in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

  15. Part 2: Ctrough of anti-HER3-ac-DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

  16. Part 2: Ctrough of DXd in plasma

    Time frame: At designated timepoints (up to approximately 5 years)

    Blood samples will be collected at specified intervals for the determination of Ctrough.

Study contacts

Contact information is provided by the study sponsor or research team.

Toll Free Number

CONTACT

[email protected]

1-888-577-8839

Sponsors and collaborators

Lead sponsor

Merck Sharp & Dohme LLC

Industry

Collaborators

  • Daiichi Sankyo

Registry information

Official study title

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

Important dates

Study start
2025
Primary completion
2030
Study completion
2030
First posted
Apr 23, 2025
Registry last updated
Jul 17, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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