Geographical variations in the incidence of childhood acute leukaemia in France over the period 1990-2004.

Spatial variations in childhood acute leukaemia (AL) incidence rates were investigated by département, in mainland France, over the period 1990-2004. This is the first spatial study of this incidence to cover a 15-year period. French National Registry of Childhood Haematological Malignancies data and population counts by type of leukaemia (AL, acute lymphoblastic leukaemia, acute myeloblastic leukaemia), time period (1990-2004, 1990-1994, 1995-1999 and 2000-2004), sex, and age group (0-14, 0-4, 5-9 and 10-14 years of age) were considered. The overall homogeneity of the relative risks of leukaemia was tested, as well as comparison to 1 of each relative risk by the exact Poisson test. To give a more stable estimate of the underlying relative risk pattern than that provided by the local standardized incidence ratios (SIRs), Bayesian hierarchical models using four different spatial priors have been produced: the parametric BYM and CAR models, and two semiparametric models. Very slight overall heterogeneity was observed on the whole AL data set (SIR overdispersion 18.6%, P=0.10). Irrespective of the model, the ranges of the smoothed SIRs exhibited considerable shrinkage relative to the ranges of the local SIRs. The associated maps were slightly heterogeneous; the smoothed SIRs of overall acute lymphoblastic leukaemia of the south-west départements were slightly higher than those of the north-east. The results, however, did not remain stable when investigated by leukaemia type, time period, sex or age group. No spatial heterogeneity of childhood AL incidence on the département scale was observed but that does not exclude spatial heterogeneity on other scales.