1 Department of Medicine, King Abdulaziz Medical City- National Guard Health Affairs, Riyadh, Saudi Arabia.
2 Pediatric Hematology/Oncology Department, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia.
3 Department of Biostatistics- Epidemiology and Scientific Computing, King Faisal Specialist Hospital & Research Centre, P.O. Box 3354, Riyadh, 11211 Saudi Arabia.