Geographical spread of gastrointestinal tract cancer incidence in the Caspian Sea region of Iran: spatial analysis of cancer registry data

Abstract

Background: High incidence rates of gastrointestinal tract cancers have been reported in the Caspian region of Iran. This study aimed to: 1) describe the geographical spatial patterns of gastrointestinal tract cancer incidence based on cancer registry data and, 2) determine whether geographical clusters of statistical significance exist.

Methods: The Babol Cancer Registry, which covers the two major northern Iranian provinces of Mazandaran and Golestan (total population = 4,484,622) was used to identify new gastrointestinal tract cancer cases during 2001 to 2005. Age-specific cancer incidence rates were calculated for 7 gastrointestinal tract cancer sites in 26 wards of the Mazandaran and Golestan provinces. Spatial autocorrelation indices, hierarchical Bayesian Poisson models, and spatial scan statistics were used in measuring the geographic pattern and clusters.

Results: There were non-random spatial patterns in esophageal and stomach cancers that were similar for both sexes. Clusters of high incidence were identified in esophageal, stomach, colorectal and liver cancer for both sexes, as well as a possible cluster of pancreas cancer in males.

Conclusion: Gastrointestinal tract cancers exhibit significant spatial clustering of risk in northern Iran. Further work is needed to relate these geographical patterns to information on potential life-style and environmental factors.

Figure 1

Geographic boundaries of wards in Mazandaran and Golestan provinces in the Caspian Sea region of Iran.

Figure 2

Relative risk (RR) categories.

Figure 3

Spatial pattern, local clusters (wards shaded with "dots" indicate the most likely clusters, and wards shaded with "slashes" indicate the secondary clusters), and smoothed RR of esophageal cancer incidence.

Figure 4

Spatial pattern, local clusters (wards shaded with "dots" indicate the most likely clusters, and wards shaded with "slashes" indicate the secondary clusters), and smoothed RR of stomach cancer.

Figure 5

Spatial pattern, local clusters (wards shaded with "dots" indicate the most likely clusters, and wards shaded with "slashes" indicate the secondary clusters), and smoothed RR of colorectal cancer.

Figure 6

Spatial pattern, local clusters (wards shaded with "dots" indicate the most likely clusters, and wards shaded with "slashes" indicate the secondary clusters), and smoothed RR of liver cancer.