Abstract
BackgroundThe availability of geographic information from cancer and birth defect registries has increased public demands for investigation of perceived disease clusters. Many neighborhood-level cluster investigations are methodologically problematic, while maps made from registry data often ignore latency and many known risk factors. Population-based case-control and cohort studies provide a stronger foundation for spatial epidemiology because potential confounders and disease latency can be addressed.MethodsWe investigated the association between residence and colorectal, lung, and breast cancer on upper Cape Cod, Massachusetts (USA) using extensive data on covariates and residential history from two case-control studies for 1983–1993. We generated maps using generalized additive models, smoothing on longitude and latitude while adjusting for covariates. The resulting continuous surface estimates disease rates relative to the whole study area. We used permutation tests to examine the overall importance of location in the model and identify areas of increased and decreased risk.ResultsMaps of colorectal cancer were relatively flat. Assuming 15 years of latency, lung cancer was significantly elevated just northeast of the Massachusetts Military Reservation, although the result did not hold when we restricted to residences of longest duration. Earlier non-spatial epidemiology had found a weak association between lung cancer and proximity to gun and mortar positions on the reservation. Breast cancer hot spots tended to increase in magnitude as we increased latency and adjusted for covariates, indicating that confounders were partly hiding these areas. Significant breast cancer hot spots were located near known groundwater plumes and the Massachusetts Military Reservation.DiscussionSpatial epidemiology of population-based case-control studies addresses many methodological criticisms of cluster studies and generates new exposure hypotheses. Our results provide evidence for spatial clustering of breast cancer on upper Cape Cod. The analysis suggests further investigation of the potential association between breast cancer and pollution plumes based on detailed exposure modeling.
Highlights
The availability of geographic information from cancer and birth defect registries has increased public demands for investigation of perceived disease clusters
Study Population We investigated the association between residence and breast, lung and colorectal cancer on Upper Cape Cod, Massachusetts (USA) using data from population-based case-control studies [10,11,12]
Our analyses showed little or no association between geographical location and colorectal cancer on upper Cape Cod
Summary
The availability of geographic information from cancer and birth defect registries has increased public demands for investigation of perceived disease clusters. Local disease mapping ("cluster") investigations are often desired by concerned communities, but many epidemiologists resist the pressure to search for environmental causes of clusters Critics argue that such studies are unproductive and flawed because they often combine unrelated diseases, apply arbitrary or even "gerrymandered" boundaries, contain insufficient numbers of cases, and ignore population density, latency, and known risk factors [1]. Data based on cancer registries are generally mapped by town of diagnosis (or other geographic unit) and contain limited data on covariates. This results in poor spatial resolution, potential spatial confounding, and the inability to consider latency. Cluster investigations can be an important part of responding to public concerns, even if no new etiologic knowledge is gained [3,4]
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