Substudy 01A: Zilovertamab Vedotin in Pediatric and Young Adult Participants With Hematologic Malignancies or Solid Tumors (MK-9999-01A/LIGHTBEAM-U01)

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

Inclusion Criteria:

• For hematological malignancies: Confirmed diagnosis of B-precursor B-ALL orDLBCL/Burkitt lymphoma according to World Health Organization (WHO) classificationof neoplasms of the lymphoid tissues.

• For solid tumor malignancies: Histologically confirmed diagnosis of neuroblastoma orEwing sarcoma.

Exclusion Criteria:

• History of solid organ transplant.

• Clinically significant (ie, active) cardiovascular disease.

• Known history of liver cirrhosis.

• Ongoing Grade >1 peripheral neuropathy.

• Demyelinating form of Charcot-Marie-Tooth disease.

• Diagnosed with Down syndrome.

• Ongoing graft-versus-host disease (GVHD) of any grade or receiving systemic GVHDtreatment or prophylaxis.

• History of human immunodeficiency virus (HIV) infection.

• Contraindication or hypersensitivity to any of the study intervention components.

• Received prior radiotherapy within 4 weeks of start of study intervention.Participants must have recovered from all radiation-related toxicities.

• Ongoing, chronic corticosteroid therapy (exceeding 10 mg daily of prednisoneequivalent). Prednisone equivalent dosing must have been stable for at least 4 weeksbefore Cycle 1 Day 1 (C1D1).

• Received a strong cytochrome P450 3A4 (CYP3A4) inhibitor within 7 days or a strongCYP3A4 inducer within 14 days before the start of study intervention or expectedrequirement for chronic use of a strong CYP3A4 inhibitor or inducer during the studyintervention period and for 30 days after the last dose of study intervention

• Received prior systemic anticancer therapy including investigational agents within 4weeks before the first dose of study intervention (except for prophylacticintrathecal chemotherapy and/or cytoreductive therapy with steroids/hydroxyurea.

• Received a live or live-attenuated vaccine within 30 days before the first dose ofstudy intervention. Administration of killed vaccines is allowed.

• Has received an investigational agent or has used an investigational device within 4weeks prior to study intervention administration.

• Known additional malignancy that is progressing or has required active treatmentwithin the past 1 year.

• Active infection requiring systemic therapy.

• Known history of Hepatitis B or known active Hepatitis C virus infection.

• Participants who have not adequately recovered from major surgery or have ongoingsurgical complications.