MK-9999-U01C (rhabdomyosarcoma, hepatoblastoma)
Clinical study of patritumab deruxtecan for the treatment of rhabdomyosarcoma (muscle tumor) and hepatoblastoma (liver tumor) in children between 1 month and 18 years of age.
Recruiting
Who can participate
Children with rhabdomyosarcoma (muscle tumor) or hepatoblastoma (liver tumor)
Age: 1 month to 18 years
Goal
This study uses patritumab deruxtecan. Patritumab deruxtecan is still being studied. It can only be used by participants in a study and cannot be prescribed by doctors outside a study. That is why it is called an investigational drug. Patritumab deruxtecan is also known as MK-1022 and HER3-DXd.
The goals of this study are:
To evaluate how safe the investigational drug is.
To test the investigational drug at different dose levels. This helps determine the right dose for further research.
Further research may take place within this study or in other medical scientific studies:
To evaluate how well the investigational drug works.
To determine what happens to the investigational drug in the body.
Background
Your doctor has explained what disease you or your child has. More research is needed on the treatment of these diseases in children and adolescents.
Proteins are found in and on the cells of our body. They are important for many processes in the body. HER3 is one of the many proteins found on cancer cells. The amount of HER3 may be increased in different types of cancer.
The investigational drug (patritumab deruxtecan) can recognize HER3. This allows the investigational drug to bind to the diseased cells. Once it has bound to the diseased cell, chemotherapy is delivered directly into that cell to kill it.
Chemotherapy causes fast-growing and rapidly dividing cells to die. These are usually cancer cells. Chemotherapy can also affect cells surrounding the diseased cells. The investigational drug may also damage healthy cells in the body.
In order to participate in a study please refer to your/your child’s doctor.
For international patients: please feel welcome to contact our International Patients Office.
Last reviewed
January 15, 2026
Study details
- Study details
Official 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
Cancer type
Rhabdomyosarcoma
Hepatoblastoma
Phase
1/2
Maximum number of participants
33-50, of whom 1 is expected to participate in the Netherlands
Start date
January 15, 2026
Status
Open
Local principal investigator
Dr. N.K.A van Eijkelenburg
Sponsor
Merck, Sharp & Dohme
Approval
The study of this new treatment has been reviewed by the Central Committee on Research Involving Human Subjects (CCMO). This committee has decided that it is justified to ask patients to participate in this study.
More information can be found at: CCMO
Trial registry number
Eu Clinical Trials (CTIS): 2024-518771-66
After completion of the study, you will find a summary of the results in plain language on the EU websites. You can find the study by searching for MK-9999-01C or 2024-518771-66.
The above information is intended as a brief summary only and may not reflect the most up-to-date information. For full details and the current status of a protocol, physicians can contact the Princess Máxima Center directly.