Zoledronate to Prevent Bone Health Complications in Pediatric Hematopoietic Stem Cell Transplant Survivors

Inclusion Criteria: * Patients ≥5 and ≤18 years old who are preparing for HSCT with a height-for-age corrected DXA Z-score of \<-2.0 and admitted to a CCHMC inpatient unit. * Patients ≥5 and ≤18 years old recovering from HSCT and who have developed de novo acute or chronic GVHD and are admitted to a CCHMC inpatient unit. Exclusion Criteria: * Age \<5 years and \>18 years * Patients with Fanconi anemia or other radiation-sensitive syndromes with increased malignancy risk * history of prior bisphosphonate use * low 25-OH vitamin D levels (\<20 ng/mL) * active febrile illness * uncontrolled infection * Elevated creatinine at the time of enrollment, history or renal failure, or documented low glomerular filtration rate (GFR≤90) * Active bone disease including history of abnormal PTH level for any reason, active bone fracture/healing, or primary disorder of bone development or metabolism. * Women who are pregnant or breast feeding.