Claudio Galvao de Castro1, Lauro Jose Gregianin2,3, Jan A Burger4. 1. Santa Casa de Porto Alegre, Porto Alegre, RS, Brazil. 2. Hospital de Clínicas de Porto Alegre, Porto Alegre, RS, Brazil. 3. Pediatric Department, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil. 4. Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.