Can what kids eat during cancer treatment change outcomes? new study aims to find out

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: Age: ALL and favorable biology brain tumors: Patient must be between 3 years and 21 years of age at the time of consent. Diagnosis: * ALL: Patients must have newly diagnosed B-cell ALL, T-cell ALL, or mixed phenotype acute leukemia confirmed by immunophenotyping by flow cytometry. * Brain tumors: Patients must have newly diagnosed favorable biology brain tumor confirmed by either pathology report, imaging and/or biochemical studies including low-grade gliomas, medulloblastoma, ependymoma, pituitary tumors, germ cell tumors. Treatment: * ALL and brain tumors: Participants may be children on a clinical trial or "as per" a clinical trial. * ALL: Patients will receive standard leukemia treatment. * Brain tumors: Patients will be treated depending upon standard approach with surgery, chemotherapy, radiation therapy. Patients receiving autologous stem cell transplantation as part of their regimen may be included. Location: ALL and brain tumors: Patients must be receiving treatment at one of the participating centers. Timing: * ALL: Parents/guardians must consent and patient assent, if applicable, within three working days of diagnosis. * Brain tumors: Parents/guardians must consent and assent, if applicable, prior to initiation of chemotherapy, radiation or stem cell transplant. Exclusion Criteria: ALL and brain tumors: * Patients with relapsed or progressive disease, exclusive of patients with unresectable low-grade gliomas who have progressive disease. * Patients with history of other primary malignancy. * Patients with other medical conditions not associated with the malignancy that may interfere with nutritional status/growth and/or microbiome composition, like patients with Down's syndrome, metabolic disorders or celiac disease. Patients with genetic predisposition that may interfere with nutritional status/growth. ALL: * Patient plans to receive hematopoietic stem cell transplant. * Mixed lineage leukemias who receive AML-based protocols. Brain tumors: Children/adolescents who will be managed by observation or surgery only, or diagnosed with ATRT or high-grade gliomas.