Oral Selenium Therapy for the Prevention of Mucositis

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