"A Safety and Pharmacokinetic Study of Single Agent REGN2810 in Pediatric Patients with Relapsed or Refractory Solid or Central Nervous System (CNS) Tumors and a Safety and Efficacy Trial of REGN2810 in Combination with Radiotherapy in Pediatric Patients with Newly Diagnosed Diffuse Intrinsic Pontine Glioma, Newly Diagnosed High-Grade Glioma, or Recurrent High-Grade Glioma"

Phase 1:

- To confirm the safety and anticipated recommended phase 2 dose (RP2D) of REGN2810
(cemiplimab) for children with recurrent or refractory solid or Central Nervous System
(CNS) tumors

- To characterize the pharmacokinetics (PK) of REGN2810 given in children with recurrent
or refractory solid or CNS tumors

Phase 2 (Efficacy Phase):

- To confirm the safety and anticipated RP2D of REGN2810 to be given concomitantly with
conventionally fractionated or hypofractionated radiation among patients with newly
diagnosed diffuse intrinsic pontine glioma (DIPG)

- To confirm the safety and anticipated RP2D of REGN2810 given concomitantly with
conventionally fractionated or hypofractionated radiation among patients with newly
diagnosed high-grade glioma (HGG)

- To confirm the safety and anticipated RP2D of REGN2810 given concomitantly with
re-irradiation in patients with recurrent HGG

- To assess PK of REGN2810 in pediatric patients with newly diagnosed DIPG, newly
diagnosed HGG, or recurrent HGG when given in combination with radiation

- To assess anti-tumor activity of REGN2810 in combination with radiation in improving
overall survival at 12 months (OS12) among patients with newly diagnosed DIPG

- To assess anti-tumor activity of REGN2810 in combination with radiation in improving
progression-free survival at 12 months (PFS12) among patients with newly diagnosed HGG

- To assess anti-tumor activity of REGN2810 in combination with radiation in improving
overall survival at OS12 among patients with recurrent HGG

Key Inclusion Criteria:

1. Age 0 to <18 years of age (Phase 1)

2. Age ≥3 and ≤25 years of age (Efficacy Phase)

3. Karnofsky performance status ≥50 (patients >16 years) or Lansky performance status ≥50
(patients ≤ 16 years)

4. Life expectancy >8 weeks

5. Adequate Bone Marrow Function

6. Adequate Renal Function

7. Adequate Liver Function

8. Adequate Neurologic Function

Key Exclusion Criteria:

1. Patients with bulky metastatic disease of the CNS causing Uncal herniation or
symptomatic midline shift, significant, symptomatic mass effect, or uncontrolled
neurological symptoms such as seizures or altered mental status

2. Patients with metastatic spine disease and gliomatosis as documented by diffuse
involvement of >2 lobes

3. Patients who are receiving any other investigational anticancer agent(s)

4. Patients on greater than dexamethasone 0.1 mg/kg/day (maximum 4 mg/day) or equivalent
dose in alternate corticosteroid, or actively undergoing corticosteroid dose
escalation in the last 7 days

5. Patients with a history of allogeneic stem cell transplant

6. Prior treatment with an agent that blocks the PD-1/PD-L1/PD-L2 pathway

Note: Other protocol-defined Inclusion/Exclusion criteria apply