A Study to Evaluate the Safety and Pharmacokinetics of Eflapegrastim in Pediatric Participants With Solid Tumors or Lymphomas and Treated With Myelosuppressive Chemotherapy

Inclusion Criteria: 1. Participant must have a pathologic/histologic confirmed newly diagnosed/relapsed/recurrent solid tumor or lymphoma without bone marrow involvement. 2. Participant must be a candidate to receive myelosuppressive chemotherapy, with a febrile neutropenia rate of at least 20% as outlined in the National Comprehensive Cancer Network (NCCN) guidelines. 3. Participant has adequate hematological, renal, and hepatic function. 4. Participant must have an echocardiogram (ECHO) or multigated acquisition (MUGA) within 14 days of Screening if receiving a cardiotoxic therapy and have a cardiac ejection fraction of \>50%. 5. Participant must have a lumbar puncture, if clinically indicated, to rule out central nervous system (CNS) involvement within 14 days of study entry. 6. Participant has a Karnofsky performance level ≥50% for patients ≥16 years of age or a Lansky performance level ≥50 for children \<16 years of age. Exclusion Criteria: 1. Participant has an uncontrollable infection, has an underlying medical condition, and/or another serious illness that would impair the ability of the participant to receive protocol-specified treatment. 2. Participant has had previous exposure to filgrastim (within 7 days), pegfilgrastim (within 14 days), or other granulocyte colony stimulating factor (G-CSF) products in clinical development within 2 weeks prior to the administration of study drug (eflapegrastim) 3. Participant requires concurrent radiation therapy specifically in Cycle 1. 4. Participant has had prior bone marrow or hematopoietic stem cell transplant and/or has concurrent bone marrow involvement in their malignancy, including leukemia. 5. Participant has had spinal radiation therapy within 30 days prior to study enrollment. 6. Participant has used any investigational drugs, biologics or devices within 30 days prior to study treatment or plans to use any of these during the study. 7. Participant has a known sensitivity or previous reactions to any of the G-CSF products. 8. Participant with active CNS disease. 9. Participant has not recovered from previous treatment adverse events to ≤Grade 1.