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 or DLBCL/Burkitt lymphoma according to World Health Organization (WHO) classification of neoplasms of the lymphoid tissues. * For solid tumor malignancies: Histologically confirmed diagnosis of neuroblastoma or Ewing 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 GVHD treatment 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 prednisone equivalent). Prednisone equivalent dosing must have been stable for at least 4 weeks before Cycle 1 Day 1 (C1D1). * Received a strong cytochrome P450 3A4 (CYP3A4) inhibitor within 7 days or a strong CYP3A4 inducer within 14 days before the start of study intervention or expected requirement for chronic use of a strong CYP3A4 inhibitor or inducer during the study intervention period and for 30 days after the last dose of study intervention * Received prior systemic anticancer therapy including investigational agents within 4 weeks before the first dose of study intervention (except for prophylactic intrathecal chemotherapy and/or cytoreductive therapy with steroids/hydroxyurea. * Received a live or live-attenuated vaccine within 30 days before the first dose of study intervention. Administration of killed vaccines is allowed. * Has received an investigational agent or has used an investigational device within 4 weeks prior to study intervention administration. * Known additional malignancy that is progressing or has required active treatment within 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 ongoing surgical complications.