Spatial clusters of cancers in Illinois 1986-2000.

Elevated cancer rates in some areas may arise simply by chance. The pattern generally warrants a study only when it is statistically significant. This research uses a recently developed spatial statistic, implemented in a Geographic Information System (GIS) environment, to detect spatial clusters of diagnostically specific cancers in Illinois. On the basis of the cancer incidence data (the 1986-1990 and 1996-2000 data sets) from the Illinois Cancer Registry, the study examines different clustering patterns of four leading types of cancer in Illinois, namely breast, lung, colorectal, and prostate cancers. The first part of the study uses the data at the county level, and the second part uses the data in zip code areas. The analysis using the zip code area data directly may be problematic since the rate estimates for rare events like cancer in small populations are susceptible to data errors. The spatial order method is used to group zip code areas so that the new geographic areas have sufficiently large base populations for estimates of reliable cancer rates. Results from the spatial cluster analysis may be valuable for other researchers to design follow-up case-control and retrospective cohort studies.