Blood Samples to Identify Biomarkers in Patients Treated With Cyclophosphamide After Donor Stem Cell Transplant

"Ancillary-Correlative" study type PRIMARY OBJECTIVES: I. To determine whether endogenous metabolomics compounds obtained before cyclophosphamide administration can predict the ratio of 4hydroxycyclophosphamide to cyclophosphamide area under the curve (4HCY/CY AUC). II. To evaluate mathematic models of CY and mycophenolic acid (MPA) pharmacokinetics and develop mathematic models including these pharmacokinetics, -omics data and clinical outcomes. SECONDARY OBJECTIVES: I. To assess if recipients' metabolomics and pharmacokinetics (e.g., CY and its metabolites AUCs) are associated with acute graft versus host disease (GVHD) and other clinical outcomes. II. To assess the association of the intestinal microbiome with the plasma metabolome, acute GVHD and other clinical outcomes. III. To obtain donor blood samples at one time pre-transplant and assess if donors' metabolomics are associated with acute GVHD and other clinical outcomes. EXPLORATORY OBJECTIVE: I. Donor and recipient germline deoxyribonucleic acid (DNA) isolation and genomic analysis. OUTLINE: Participants are assigned to 1 of 2 arms. ARM I (PATIENTS RECEIVING A HAPLOIDENTICAL TRANSPLANT): Patients undergo collection of blood prior to transplant, on day 0, days 3-7, day 14, and day 21. Patients also undergo collection of saliva prior to transplant and collection of stool prior to and post-transplant. Donors undergo collection of blood and saliva within 8 weeks prior to donation.