Abstract • 57

Myelodysplastic syndromes (MDS) are considered to be a very rare disease in children. After Chernobyl catastrophe the population of Belarus was exposed by potentially dangerous doses of radiation. The aims of the study was to conduct a population based study in Belarus from 1994 - 1998 and to collect basic clinical and laboratory information on a number of unselected and probably consecutive childhood MDS following the accident. Between January 1994 and December 1998 patients with features of MDS aged less than 15 years were included into study. The diagnosis were based on clinical findings; morphology according to FAB with or without the presence of cytopenia and maturation abnormalities in one or more haematopoietic cell lineage. Bone marrow karyotype was determined by routine G-banding technique and by short-term cultures. Median presentation age was 6 years(y) 9 months(m) (range 1y2m - 14 y9m) and 15 were of male gender. Classical MDS was diagnosed in 23 cases (RA - 3, RAEB - 6, RAEB-t - 3, CMML - 8) but was unclassifiable in 3. Being the only reference center of the country the incidence of MDS is following 1994 - 1.3 / mln, 1995 - 2.7 / mln, 1997 - 1.9 / mln, 1998 - 2.9 / mln (average 2.12 / mln or 5% acute leukemias). Marrow hypoplasia (defined as <30% of intertrabecular space occupied by haematopoietic tissue) was observed in 8 ( 35%) children and was present in all morphological groups including CMML (n=2). Karyotype was available in 20 children, it was normal in 8 and abnormal in 12 with monosomy7 the dominant abnormality (n=5) and in addition in one t(5;17) (q23; p13). In conclusion, the incidence of childhood MDS in Belarus is higher than generally described in European studies. In addition, hypoplastic bone marrow was present in 1/3 of cases and MDS was unclassified in 11%. Therefore, FAB classification is not suitable for all cases of childhood MDS.