We describe the demographic and biological characteristics of 1,459 children with acute leukemia in Brazil to compare the effect of immunophenotypic differences with environmental factors that might be involved in the etiology of acute lymphoblastic leukemia (ALL). Combined morphological and immunological classifications were available for 96% of cases. Of these, 55% were B cell precursor ALL comprising pro-B ALL and c-ALL, 15% T-ALL and 1.6% mature B-ALL. The proportion of Bp and T-ALL differed by race with 59% of whites being Bp-ALL and 60.7% of non-whites being T-ALL. Further inspection of these data revealed that the proportions of whites in each type (Bp/T-cell ALL) are almost identical in older children (60.3% and 59.3% respectively) but differ substantially in younger cases (< 6 years) with 63.6% of Bp-ALL and 37.3% of T-ALL being white. These results are consistent with excess incidence rates of Bp-ALL in young white children, although the distribution of Bp-ALL and T-ALL in each region was equitable with non-significant differences. The incidence rate of ALL was geographically variable, such as 2.2, 2.6 and 3.3/10(5) per year in Bahia, Rio and Brasilia, respectively. To evaluate if the pick of incidence could be related to viral infection, we observed that Bp-ALL was ascendant from late summer to winter and decreased in spring, whereas T-ALL had an increased peak in the fall. This study also provides background information for the epidemiology of childhood ALL in Brazil in which c-ALL could be associated with timing of exposure to infection and requires further investigations.
Acute lymphoblastic leukemia; mmunophenotyping; ethnic origin; epidemiology
