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Safety and Efficacy of Ifinatamab Deruxtecan in Pediatric Patients Under 18 With Relapsed or Refractory Solid Tumors

Verified siteInvestigationalNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study looks at children under 12 who have cancers that have come back (relapsed) or did not respond to standard treatments (refractory). These are called solid tumors, which include types such as neuroblastoma, rhabdomyosarcoma, Wilms tumor, and osteosarcoma. The investigational medicine is Ifinatamab Deruxtecan, also known by the code name MK-9999-01D, given by intravenous infusion (a medicine slowly dripped into a vein).

The main aim is to see if the drug is safe and can shrink or stop the growth of these cancers. Children will receive the medicine in a series of visits where doctors check for side effects, adjust the dose if needed, and use simple scans to see whether the tumor is getting smaller. The study follows participants for several months to record any problems and to determine whether the cancer responds, using terms like “objective response rate” (the percentage of children whose tumors shrink) and “disease control” (tumors that stay the same size or get smaller).

The research process

The trial runs in 10 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline evaluation

    After joining the study you will have a physical examination, blood tests, and imaging studies to document the current status of your cancer.

    The results will be used to determine eligibility for the treatment phases.

  2. Step 2

    First infusion (part 1)

    You will receive ifinatamab deruxtecan as an intravenous infusion in a clinical setting.

    The exact dose and schedule are defined by the study protocol and will be administered by trained staff.

  3. Step 3

    Monitoring for dose-limiting toxicity

    Following each infusion you will be observed for a period of time to detect any dose-limiting toxicity, which are serious side effects that may require a change in dose.

    Regular laboratory tests and clinical assessments will be performed during this monitoring period.

  4. Step 4

    Dose adjustment if needed

    If an adverse event occurs, the study team may modify the dose of ifinatamab deruxtecan according to predefined rules.

    The goal is to maintain safety while allowing continued treatment.

  5. Step 5

    Subsequent infusion cycles

    You will receive additional infusions of ifinatamab deruxtecan at regular intervals specified in the protocol (for example, every three weeks).

    Each cycle includes the infusion itself followed by safety monitoring.

  6. Step 6

    Tumor response assessment

    Periodic imaging studies will be performed to evaluate the effect of the treatment on the tumor.

    The response will be classified using standard criteria such as objective response rate and disease control at four months.

  7. Step 7

    Ongoing safety evaluations

    Throughout the study you will have regular visits for physical exams, blood tests, and questionnaires to capture any new or worsening adverse events.

    These evaluations help determine whether the treatment remains safe for you.

  8. Step 8

    Transition to part 2 (if applicable)

    If the safety profile is acceptable and the tumor shows a response, you may continue into part 2 of the study, which focuses on further efficacy evaluation.

    The same infusion schedule and monitoring procedures continue in this phase.

  9. Step 9

    Treatment discontinuation criteria

    Treatment may be stopped if you experience severe adverse events that cannot be managed, if the disease progresses, or if you choose to discontinue.

    The decision will be based on clinical judgment and predefined study rules.

  10. Step 10

    Final follow‑up

    After the last infusion you will have scheduled follow‑up visits to assess long‑term outcomes such as overall survival and any late side effects.

    These visits may include physical examinations, laboratory tests, and imaging as required by the study.

Who can join the trial?

4 criteria

  • Has a cancer that has come back or gotten worse after prior treatment (recurrent or relapsed) and does not respond to standard medicines (refractory). For Part 1, the cancer must be a solid tumor that is not in the brain or spinal cord (excluding primary CNS). For Part 2, the cancer must be one of osteosarcoma, neuroblastoma, rhabdomyosarcoma, or Wilms tumor, and this must be confirmed by looking at the tumor tissue under a microscope (histologically confirmed).
  • Must have documented growth of the tumor on imaging studies (radiological disease progression) after at least one previous treatment plan (line of prior therapy) for cancer that is locally advanced or has spread (metastatic), and there must be no other satisfactory treatment options available.
  • Must be a child of any sex or gender who is at least 1 month old but younger than 12 years for Part 1, or younger than 18 years for Part 2, at the time of giving consent or assent (informed consent for parents/guardians and assent for the child when appropriate).
  • Any side effects from previous cancer treatments (adverse events or AEs) must have improved to mild or none (≤Grade 1) or returned to baseline. If the side effects involve hormone problems, they must be controlled with hormone replacement therapy. Mild nerve problems (≤Grade 2 neuropathy) or mild hair loss (≤Grade 2 alopecia) are also acceptable.

Who cannot join the trial?

14 criteria

  • Corneal disease: Significant problems with the clear front part of the eye that affect vision.
  • Human immunodeficiency virus (HIV) infection: Having HIV, the virus that can weaken the immune system.
  • Additional malignancy that is getting worse or needed active treatment within the past year: Another cancer that has progressed or required therapy in the last 12 months.
  • Active infection that requires systemic therapy: A current infection needing medicine taken by mouth or through the bloodstream.
  • Known hypersensitivity or contraindication to the study drug or its inactive ingredients: An allergy or a medical reason not to use the medication.
  • Not fully recovered from major surgery or having ongoing surgical complications: Still healing or having problems after a big operation.
  • History of cerebrovascular accident (stroke), transient ischemic attack (brief stroke), or another arterial blood‑clot event within the past six months.
  • Uncontrolled or significant cardiovascular disease, including abnormal heart rhythms (conduction abnormalities), high blood pressure (hypertension), blocked heart arteries (ischemic heart disease), weak heart pumping (heart failure), or poor blood flow in the limbs (peripheral vascular disease).
  • History, current presence, or suspected interstitial lung disease (ILD) or pneumonitis (lung inflammation), including cases caused by medication, that cannot be ruled out by imaging.
  • Severe breathing problems (respiratory compromise) caused by other lung illnesses happening at the same time.
  • Active, known, or suspected autoimmune disease: A condition where the immune system attacks the body, such as lupus or rheumatoid arthritis.
  • History of solid organ transplant: Having received a transplanted organ like a kidney, liver, or heart.
  • History of allogeneic stem cell transplant (SCT): Having had a stem cell transplant from a donor.
  • Current cancer spread to the brain or spinal cord (CNS metastases), cancer in the lining of the brain (carcinomatous meningitis or leptomeningeal disease), or pressure on the spinal cord (spinal cord compression). Untreated, symptom‑free brain metastases are allowed only if they have been radiologically stable (no growth on scans) for at least four weeks.
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Investigated drugs

Ifinatamab Deruxtecan is an experimental medicine being tested in children with solid tumors that have come back or did not respond to other treatments. It is given through an IV (a needle into a vein) as a liquid that is slowly infused. In this study, doctors are looking at how safe the drug is for young patients, how well they can tolerate it, and what dose is appropriate. They are also checking whether the medicine can shrink or stop the growth of tumors such as neuroblastoma, rhabdomyosarcoma, Wilms tumor, or other solid tumors, by measuring the tumor’s response during the trial.

What is already known about the treatment

Ifinatamab Deruxtecan - It is given as an intravenous infusion, using a clear solution that is slowly dripped into a vein. The drug is still investigational and is being studied in early‑stage clinical trials; it has not yet received regulatory approval. It is being tested for children with relapsed or refractory solid tumors such as neuroblastoma, rhabdomyosarcoma, Wilms tumor, and other solid cancers. The medicine works as an antibody‑drug conjugate: the antibody part finds and binds to a protein on cancer cells, then delivers the attached chemotherapy (deruxtecan) that damages the cell’s DNA and kills the tumor. It belongs to the class of targeted antineoplastic agents known as antibody‑drug conjugates.

Investigated diseases

  • Neuroblastoma

    A cancer that begins in nerve cells of the adrenal glands or along the sympathetic nervous system, most often in infants and young children. It forms a solid tumor that can enlarge the affected area. As it grows, the tumor may spread to nearby lymph nodes, bone marrow, or other organs. The disease can appear as a painless lump or cause abdominal discomfort. Over time, the tumor may become larger and affect the function of nearby structures.

  • Rhabdomyosarcoma

    A cancer that arises from skeletal muscle tissue, occurring in children and adolescents. It typically creates a firm mass in the head, neck, genitals, or limbs. The tumor can expand locally, pushing against surrounding muscles and nerves. It may also travel through the bloodstream to distant sites such as lungs or bones. The growth pattern often leads to increasing size and possible interference with normal movement.

  • Wilms tumor

    A kidney cancer that develops in children, originating from immature kidney cells. It usually presents as a swelling or mass in the abdomen. As the tumor enlarges, it can distort the shape of the kidney and press on nearby organs. The disease may extend beyond the kidney into surrounding tissues or lymph nodes. Continued growth can affect kidney function and cause abdominal discomfort.

  • Osteosarcoma

    A bone cancer that most commonly starts in the long bones near the knee in teenagers. It creates a hard, painful mass that weakens the bone. The tumor can break through the bone surface and invade surrounding soft tissue. Cancer cells may travel through the bloodstream to the lungs or other bones. Over time, the lesion may enlarge, causing fractures or reduced mobility.

Trial detailsLast updated 7 Oct 2026
Age0-17PhasePhase ITrial ID2025-522339-32-00Protocol codeMK-9999-01DEstimated enrolment78 patientsSponsorMerck Sharp & Dohme LLC

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