An assessment of spatial clustering of leukaemias and lymphomas among young people in New Zealand

Study objective-To assess spatial clustering of childhood leukaemias and ly mphomas in New Zealand, using a national dataset from a country with no nuc lear installations. Design-New Zealand Map Grid coordinates, derived from the birth addresses o f cases and controls were used in clustering analyses that applied Cuzick a nd Edwards' method. Setting-The whole of New Zealand. Participants-The cases were ascertained from the New Zealand Cancer Registr y. They were diagnosed with leukaemia or lymphoma at ages 0-14 years during the period 1976 to 1987. For Hodgkin's disease, the age range was extended to include those aged from 0-24 years. The cancer registrations were linke d with national birth records, to obtain the birth addresses of the cases. The controls were selected at random from birth records, with matching to c ases (1:1) on age and sex. The analyses included 600 cases and 600 controls . Main results-There was no statistically significant spatial clustering for any tumour group overall, including acute lymphoblastic leukaemia, acute no nlymphoblastic leukaemia, other leukaemias, non-Hodgkin's lymphomas, Hodgki n's disease, and all these combined. Significant clustering was found in a subanalysis for one of three age specific subgroups of acute lymphoblastic leukaemia (ages 10-14 years, p=0.003). Conclusion-The subgroup finding may have been real or a chance association, as several comparisons were made. This study found little evidence for spa tial clustering of leukaemias or lymphomas in a population with no nuclear installations.