Time trends and seasonal variations in the diagnosis of childhood acute lymphoblastic leukaemia in France

Background: Several studies have evidenced an increase in the incidence of childhood leukaemia since the 1970s but the variations since 2000 have received little attention. Seasonal variations in incidence have also been widely investigated, with however inconsistent conclusions. The present study aimed to investigate jointly the temporal trends and the seasonal variations in the month of diagnosis of childhood acute lymphoblastic leukaemia (ALL). Methods: All the cases of ALL registered in the French National Registry of Childhood Haematological malignancies during 1990–2007 were included in the study. The overall temporal trend and seasonality of ALL were tested with Poisson regression models on 0–14-year-old ALL cases, and specifically on the B-cell precursor ALL (Bcp-ALL) cases. The analyses were also stratified by age groups and gender. Results: Over 1990–2007, a significant time trend in risk of +0.48% (0.02–0.95%) per year for all ALL and +0.85% (0.33–1.37%) for Bcp-ALL was found. The increase was more marked for 7–14-year-old girls with a trend of +2.84% (1.34–4.36%) per year for Bcp-ALL. Seasonal variations were also evidenced for 1–6-year-old boys, with a standardised incidence ratio of 1.11 (1.04–1.18) for Bcp-ALL in April, August and December. Conclusion: The study showed an increase in childhood ALL risk over 1990–2007, which tended to be stronger for 7–14-year-old Bcp-ALL, particularly in girls (about one case per year, on average). However, although in accordance with the log-linear assumption, the increase in risk seemed less marked after 2001. The study also suggested seasonal variations in the month of diagnosis for 1–6-year-old boys.