Letermovir Prophylaxis for Cytomegalovirus in Pediatric Hematopoietic Cell Transplantation
This phase III single arm trial determines whether taking prophylactic letermovir will reduce the likelihood of infection with cytomegalovirus (CMV) in children and adolescents after stem cell transplant compared to estimated rate of infection without prophylaxis. The treatments used to prepare for HCT reduce the body's natural infection-fighting ability and increase the likelihood of an infection with a virus called cytomegalovirus. Prophylaxis means to take a drug to prevent a disease or side effect. Letermovir is an antiviral drug that stops cytomegalovirus from multiplying and may prevent cytomegalovirus infection and make the disease less severe.
• \>= 2 years and \< 18 years at the time of enrollment
• Weight must be \>= 6 kg at the time of enrollment
• Planned allogeneic HCT (bone marrow, peripheral blood stem cell, or cord blood transplant)
• Patient must be CMV sero-positive (i.e., recipient CMV immunoglobulin G positive)
⁃ Note: If a patient has hypogammaglobulinemia but has previously been documented as CMV sero-positive, that is acceptable for study inclusion. For all patients already confirmed to be CMV IgG seropositive, repeat testing is not required within 7 days prior to enrollment. However, the laboratory data determining eligibility must be available in the patient's medical/research record for verification
• Patient is eligible for entry only if it is feasible for plasma CMV PCR testing to be sent and resulted within the protocol mandated time period
⁃ Reminder: To limit the likelihood of positive plasma CMV PCR post-enrollment and prior to start of study treatment period, it is recommended that patient enrollment proceed after patients start their transplant preparative regimen
• Patient must have a performance status corresponding to Lansky/Karnofsky scores \> 50
⁃ Note: Use Lansky for patients =\< 16 years of age and Karnofsky for patients \> 16 years of age. For further reference, see performance status scales scoring under the standard sections for protocols among protocol reference materials provided on the Children's Oncology Group (COG) member website: https://members.childrensoncologygroup.org/prot/reference\_materials.asp
• Estimated glomerular filtration rate \> 10 mL/min/1.73 m\^2 and not receiving dialysis
• Direct bilirubin =\< 2 mg/dL and serum glutamate-pyruvate transaminase (SPGT) (alanine transaminase \[ALT\]) =\<10 x upper limit of normal (ULN) for age
⁃ Note: For the purpose of this study, the ULN for SGPT (ALT) has been set to the value of 45 U/L