Graft-versus-host-disease (GVHD) is common complication of hematopoietic stem cell transplantation. Vitamin D deficiency has been shown to be associated with increased risk of chronic GVHD in previous clinical studies. The purpose of this research is to investigate the effect of vitamin D supplementation in patients undergoing hematopoietic stem cell transplantation

Hematopoietic stem cell transplant candidates are randomized to vitamin D supplementation or usual care. Five milligrams (200,000 IU) of cholecalciferol is injected to intervention group before stem cell transplantation. Additional supplementation of cholecalciferol during follow-up period is determined according to the level of 25(OH)D3. The primary outcome is the incidence of chronic GVHD which is determined according to IBMTR criteria. The secondary outcome consists of the incidence of acute GVHD, incidence and severity of vitamin D deficiency, and serum concentration of 25(OH)D3. Study investigators expect that supplementation of vitamin D may improve the outcome of stem cell transplantation by reducing the incidence of chronic GVHD.

Inclusion Criteria:

• Adults with ≥ 18 years old
• Diagnosed with hematologic maligancies
• Planned to undergo allogeneic stem cell transplantation

Exclusion Criteria:

• Hypercalcemia (ionized serum calcium level [iCa] > 1.3 mmol/L, corrected serum calcium level > 10.5 mg/dL)
• Impaired renal function (Serum creatinine ≥ 2.4 mg/dL)
• Not in complete remssion (except for myelodysplastic syndrome and myeloproliferative neoplasm)
• Consent withdrawal
• Considered inadequate under investigator's discretion