Spatial analysis of colorectal cancer incidence and proportion of late-stage in Massachusetts residents: 1995-1998

Background: The aims of this study were to determine if observed geographic variations in colorectal cancer incidence are simply random or are statistically significant deviations from randomness, whether statistically significant excesses are temporary or persistent, and whether they can be explained by risk factors such as socioeconomic status (SES) or the percent of the population residing in an urban area rather than a rural area. Between 1995 and 1998, 6360 male and 6628 female invasive colorectal cancer cases were diagnosed in Massachusetts residents. Cases were aggregated to Census tracts and analyzed for deviations from random occurrence with respect to both location and time. Results: Six geographic areas that deviated significantly from randomness were uncovered in the age-adjusted analyses of males: three with higher incidence rates than expected and eight lower than expected. In the age-adjusted analyses of females, one area with a higher incidence rate, and one area with a lower incidence rate than expected, were found. After adjustment for SES and percent urban, some of these areas were no longer significantly different. Conclusion: Public health practitioners can use the results of this study to focus their attention onto areas in Massachusetts that need to increase colorectal screening or have elevated risk of colorectal cancer incidence.