Intervention: Ergocalciferol
Trial phase: Phase 2
ATC code: A11CC01
SMILES: [H][C@@]12CC[C@]([H])([C@H](C)/C=C/[C@H](C)C(C)C)[C@@]1(C)CCC/C2=C\C=C1\C[C@@H](O)CCC1=C
Sex: All
Age groups: Child | Adult
Healthy volunteers: No
Participants at risk: 32
Group description: Subjects will receive a standard recommended dose of calcium and vitamin D.

Calcium and vitamin D: All subjects will receive a standard recommended dose of 600 IU/day of vitamin D. Subjects who do not meet the RDA will receive additional calcium supplementation.
Eligibility criteria:
Inclusion Criteria:

Allogeneic hematopoietic cell transplant for hematologic malignancy (i.e. leukemia, lymphoma including ALL, AML, CML, NHL, HL) in complete remission; myelodysplastic syndrome (active dysplasia and/or blasts are permitted, but must not have active leukemia) or idiopathic severe aplastic anemia (SAA)

Non-malignant diseases including idiopathic severe aplastic anemia (SAA) and other bone marrow failure disorders, hemoglobinopathies, adrenoleukodystrophy, immune deficiencies/dysregulation disorders who will be receiving myeloablative or reduced toxicity preparative regimens that meet the following criteria:

Regimens include those that are TBI based if the TBI dose is > 500cGy single dose or > 800cGy fractionated, or doses <500 cGy if combined with busulfan or treosulfan. These also include chemotherapy only based regimens that contain myeloablative doses of busulfan (>8mg/kg) or treosulfan without TBI.
Patients with severe aplastic anemia are eligible regardless of conditioning regimen
Myeloablative preparative regimen (for SAA any conditioning therapy allowed)
Male or female ≥1 but ≤ 20 years of age at time of study enrollment
Patient or parent(s)/legal guardian(s) is able and willing to provide informed consent. Assent will be obtained per local institutional policy. Subjects who turn 18 during the course of the study will be consented at that time of their next visit by a member of the research staff.

Exclusion Criteria:

History of a primary bone malignancy involving the lumbar spine
Prior and/or planned concomitant medical therapy during the study period (through Day 360 post-HCT) with other bisphosphonates, Denosumab, or Teriparatide
Pregnancy or breastfeeding - menstruating females must have a negative pregnancy test prior to study enrollment and agree to repeat pregnancy testing and contraception use per protocol as pamidronate is Pregnancy Category D - positive evidence of human fetal risk based on adverse reaction data
Renal insufficiency, defined as creatinine level greater than the upper limit of normal for age
Hereditary metabolic bone disease or skeletal dysplasia (e.g., osteopetrosis or OI) or primary hyperparathyroidism
Other indications for HCT, including Fanconi anemia, other form of inherited bone marrow failure diseases, metabolic disorder, hemoglobinopathy, or immune deficiency
Clinically significant fractures as defined by ISCD (a long bone fracture of the lower extremities, vertebral compression fracture, or two or more long bone fractures of the upper extremities) (88,89) indicated by a cast or a spine x-ray within the last 2 weeks
Known or suspected allergy to pamidronate or related products
Planned administration of an investigational study drug or agent that either can interact with pamidronate or have an independent effect on bone mineral density within the 4 weeks prior to randomization (Day 90) or planned use during study participation (Day 90 through Day 360)
Impending invasive dental procedure that would be expected to occur during study participation (through Day 360)