In Central America, nearly 70% of pediatric cancer is related to hemato-oncologic disorders, especially acute lymphoblastic leukemia (ALL). Preliminary studies have described a high incidence of childhood leukemia in these countries; however, no molecular analyses of these malignancies have yet been carried out. We studied diagnostic samples from 84 patients from the National Children's Hospital in San Jose, Costa Rica (65 precursor B-ALL, 5 T-cell ALL, and 14 acute myeloblastic leukemia). Our methodology included cytogenetic, fluorescent in situ hybridization, and polymerase chain reaction approaches. The observed rate of leukemia was 52.2 cases per million children per year. Twelve out of 65 (18.4%) precursor B-ALL tested positive for TEL-AML1 and 3 cases for BCR-ABL (4.6%). In addition, we detected 2 patients carrying an E2A-PBX1 transcript (3.1%) and 1 patient with an MLL-AF4 fusion gene (1.5%). None of the T-cell ALL cases were positive for either SIL-TAL1 or HOX11L2. Within 14 acute myeloblastic leukemia patients, we confirmed 2 cases with FLT3-internal tandem duplication+, 1 patient with AML1-ETO, and only 1 case carrying a PML-RARalpha rearrangement. The present study confirms the relatively high incidence of pediatric leukemia in Costa Rica and constitutes the first report regarding the incidence of the main molecular alterations of childhood leukemia in our region.

Cytogenetic studies in children with Acute Lymphocitic Leukemia-B in Costa Rica.Chromosome analyses were performed on bone marrow of 177 pediatric patients with Acute Lymphocitic Leukemia at the "Hospital Nacional de Niños". The standard cytogenetic techniques now belongs to the panel of mandatory analyses performed at diagnosis of our acute leukemia patients and represent a major advantage to be effective and independent prognostic factors, essential for therapeutic choices. Cytogenetic results were achieved in 83% of the bone marrow samples: normal karyotypes represented 29% and abnormal karyotypes 71% with the follow distribution: t(9;22) 3%; t(1;19) 5%; t(4;11) 3%, Hyperdiploidy 39%; other chromosomal abnormalities 21%. Systematic cytogenetic analyses are essencial to define morpho-immunologic sub-types of leukemia and to detect new translocations that allows to understand hematopoiesis and leukemogenesis. Rev.