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.