Background: Disease mapping has a long history in epidemiology. Evaluating the spatial pattern of several diseases, as well as shared and specific risk factors in mortality, is considered as one of the applications of disease mapping. Stomach, esophageal, and lung cancers are among the five most common cancers among both genders in Iran, but no study is available on the spatial distribution of their mortality rate in Iran. The present study aimed to investigate the geographical distribution of the relative risk of mortality and to define the spatial pattern of shared and specific risk factors for the above-mentioned three cancers by sharing their mortality data at the county level in Iran.
Method: This study analyzed the mortality data of stomach, esophageal, and lung cancers in Iran from March 2013 - March 2015. The Besag, York, and Mollie’s (BYM) model and Shared Component (SC) models were used for investigating the spatial changes of cancer mortality and determining the spatial pattern of their shared and specific risk factors. Data analysis was conducted using R and OpenBUGS software.
Results: The number of deaths for the esophageal, stomach, and lung cancers in Iran from March 2013 -March 2014, was 11,720 of which stomach and lung cancers were 50% and 30%, respectively. The spatial pattern of the stomach and esophageal cancer mortality was more similar to that of lung cancer due to the risk factors shared only between esophageal and stomach cancers.
Conclusion: The effects of smoking on lung cancer mortality were higher than the other two cancers. The available data indicated that esophageal cancer mortality was more affected by nutritional factors than stomach cancer mortality in Iran. The effect of nutritional factors on stomach and esophageal cancer mortality in the northern half of Iran was higher than the southern half. As a result, the relative risk of these cancers mortality in the southern half was more affected by smoking than nutritional factors.