Selenium as an antioxidant and anti-inflammatory agent could be effective in prevention of mucositis induced by chemotherapy and radiotherapy. Other agents such as vitamin E, Zinc sulfate, amifostine, beta carotene and benzidamine are indicated for prevention of mucositis and positive effects are seen. Our purpose in this double blinded randomized study is to evaluate the selenium effect on mucositis prevention in patient with acute myeloid leukemia (AML) & acute lymphoblastic leukemia (ALL) whose received Busulfan and/or Cyclophosphamide before Hematopoietic stem cell transplantation (HSCT).

Patients with AML or ALL diagnosis, candidates for high dose chemotherapy with stem cell transplantation will be screened for enrollment in the study.

Patients will be randomized in two groups with balanced block randomization method. One group will receive selenium tablet twice per day and another group will receive placebo two times per day.Therapy will start on the morning before starting chemotherapy and will continue until the first of either discharge day or day +21.

Response assessment will include:

1. Mucositis assessment using WHO grading and OMAS scores- to be done from baseline and until day +21 or discharge day if before day +21.
2. Evaluation of selenium and glutathione peroxidase levels in the serum, - to be done at baseline, day +7 and day +14.
3. Collection of clinical outcome data regarding infectious complications including- presence and length of febrile neutropenia, use of antibacterial and antifungal medications

Inclusion Criteria:

• Patients with AML or ALL undergoing high dose chemotherapy with stem cell transplantation
• Adequate renal and hepatic function

Exclusion Criteria:

• Taking selenium supplement before admission