| [Background and objectives]Esophageal cancer is a common digestive tract malignant tumor with relatively high incidence and mortality.Squamous cell carcinoma of the esophagus(ESCC)and adenocarcinoma of the esophagus(EAC)are the main two histologic types of esophageal cancer.Lots of epidemiologic studies have shown that the esophageal cancer incidence varies internationally with certain regional clustering.As one of the countries with remarkably high incidence rates of esophageal cancer,China also showed great spatial heterogeneity in esophageal cancer incidence according to related research.Studies targeted on the spatial distribution of esophageal cancer incidence and mortality indicated that the spatial distribution of esophageal cancer was significantly heterogeneous with certain regional clustering even at small spatial scale level.This finding suggested that esophageal cancer is not only associated with risk factors in individual level,but also risk factors in geographical level.Traditional case-control studies conducted in China and other countries usually restrict the living environment of the case and control to the same region(for example,the same village)to match the control with the case.In this way,the impact of some geographical environment factors on the disease may be neglected at the same time.However,ecological studies being conducted at home and abroad showed that the regional high incidence of esophageal cancer may be caused by multiple risk factors,and the influence of geographical factors cannot be ignored.Therefore,our research considered Feicheng city in Shandong province,one of the regions with high esophageal cancer incidence in China,as the study region.Esophageal cancer spatial epidemiological database was constructed based on geographic information system(GIS)by combining esophageal cancer data from the population-based cancer registry system in Feicheng city with the corresponding spatial geographic data.Also,our research put forward a research design strategy called "spatial case-control study".The main idea of the strategy is to first apply the spatial autocorrelation method to detect the spatial heterogeneity of esophageal cancer incidence,then use the spatial scan statistic to locate esophageal high incidence and low incidence clusters.By defining cases in high incidence clusters as the "case" and cases in low incidence clusters as the "control",epidemiological characteristics and geographical risk factors in high incidence region can be detected.Our research aimed to illustrate the epidemiological characteristics of esophageal cancer in Feicheng city,the epidemiological characteristics in both individual and regional levels of high risk clusters,and to detect the risk factors in geographical level based on the above analysis in order to provide a reference and scientific basis to policymakers to make effective preventive and control strategies to focus interventions on the geographic areas that can most benefit.[Design and methods]This study was conducted based on esophageal cancer data from the population-based cancer registry system in Feicheng city to obtain incidence data from 2001 to 2015.The incidence of esophageal cancer in Feicheng city was detected by describing the distribution of esophageal cancer incidence per year,by sex and age groups.Joinpoint regression analysis was applied to detect the trend of esophageal cancer incidence during the study period.Moreover,spatial statistical analyses were conducted to explore the spatial distribution characteristics of esophageal cancer in the spatial scale of village level and to locate the high/low incidence clusters.Finally,traditional logistic regression model and spatial logistic regression model were applied to detect risk factors in geographic level in the high incidence region.[Results]1.Esophageal cancer incidence in Feicheng city from 2001 to 2015:(1)There were 10740 esophageal cancer cases in Feicheng city during the study period with 7178 males and 3562 females.The number of male cases were obviously greater than female cases each year with a total sex ratio of 2.02.The crude incidence of esophageal cancer among the total population,the male population and the female population were the highest in the year of 2010 with the number of 120.50/100,000,160.78/100,000 and 81.36/100,000 respectively.The age-adjusted incidence of esophageal cancer among the total population,the male population and the female population were also the highest in the year of 2010 with the number of 107.76/100,000,146.86/100,000 and 66.75/100,000 respectively.(2)The average age of esophageal cancer cases was(63.69± 10.81)years old,(62.24± 10.38)years old for male cases and(66.60± 11.07)years old for female cases.The average age at diagnosis in female was greater than the male(P<0.0001).The incidence in both genders were relatively low before 40 years old and rose rapidly after 40.The incidence of both gender peaked at the age group of 70-80 years old and declined after 80.(3)The result of the joinpoint regression analysis of esophageal cancer crude incidence and age-adjusted incidence in Feicheng city showed that esophageal cancer incidence among the total population,the male population and the female population rose from 2001 to around 2011 and then declined during the recent few years.2.Spatial distribution characteristics of esophageal cancer in Feicheng city from 2001 to 2015:(1)The interpolation maps of esophageal cancer incidence in total population,male population and female population indicated a trend of gradient rising from northeast to southwest in esophageal cancer incidence.The low incidence region were mainly located in Laocheng town,Chaoquan town and part of Xincheng subdistrict,Wangguadian town and Yiyang town,which were all located in the northeast area of Feicheng city.Besides,the northwest region of Shiheng town(located in the northwest area of Feicheng city)and part of Bianyuan town(located in the southeast area of Feicheng city)also had relatively low incidence.The high incidence region were mainly located in the Sunbo town,Anjiazhuang town,Wenyang town and Wangzhuang town,which were all located in the southwest area of Feicheng city.There was a small-scale round high incidence area in the male population at the convergence of Yiyang town,Bianyuan town and Anlinzhan town.The scale of the high incidence region in the female population was smaller compared with the total population.(2)The result of the global spatial autocorrelation analysis showed that the Moran’s 1 among the total population,the male population and the female population were 0.3020,0.1846 and 0.2565 respectively(P<0.0001),which indicated that the distribution of esophageal cancer incidence is significantly heterogeneous at village level.(3)The result of the local spatial autocorrelation analysis showed that there were 79 high-high clusters,103 low-low clusters,20 high-low clusters and 26 low-high clusters in Feicheng city at the village level.The high incidence clusters were mainly located in Anjiazhuang town,Anlinzhan town,Hutun town,Sunbo town,Wangzhuang town and Wenyang town;the low incidence clusters were mainly located in Laocheng town,Xincheng subdistrict and Bianyuan town.(4)During the study period of 2001 to 2015,there were 6 esophageal cancer clusters with statistical significance(3 high incidence clusters and 3 low incidence clusters).The most likely high incidence cluster was located in the southwest area of Feicheng city which included 89 villages in Sunbo town,Anjiazhuang town and Wenyang town;the most likely low incidence cluster was located in the northeast area of Feicheng city which included 94 villages in Laocheng town,Wangguadian town,Chaoquan town,Xincheng subdistrict and Yiyang town.3.Analysis of risk factors in high incidence clusters in Feicheng city:(1)There were 127 villages and 3328 esophageal cancer cases in high incidence clusters.The low incidence clusters included 182 villages and 2344 esophageal cancer cases.Gender difference in esophageal cancer incidence was found in each year since incidence in male was obviously higher than in female population.The esophageal cancer incidence in high incidence region was higher than that in low incidence region from 2001-2015.Similar trends were found in both regions and both genders from 2001-2015 as the incidence rose at first and then declined.Both the high incidence clusters and the low incidence clusters had more male cases than female cases.The proportion of male cases in high incidence clusters was greater than that in low incidence clusters.The age at diagnosis in high incidence clusters were smaller than that in low incidence clusters.The difference in altitude,soil types and water monitoring indicators between high incidence and low incidence clusters showed statistical significance.(2)In the multivariate logistic analysis model in village level,negative association between altitude and high incidence of esophageal cancer was found.Positive associations between cinnamon soil,nitrate nitrogen in water,pH in water and high incidence of esophageal cancer were found.(3)Spatial logistic regression results showed that the parameter estimates of altitude,cinnamon soil,nitrate nitrogen in water and pH in water differs across the Feicheng city.Negative association between altitude and high incidence of esophageal cancer was found while positive associations between cinnamon soil,nitrate nitrogen in water,pH in water and high incidence of esophageal cancer were found during the analysis.[Conclusions]1.The esophageal cancer incidence in Feicheng city during 2001 to 2015 was 91.86 per 100,000(123.67 per 100,000 in males and 60.51 per 100,000 in females).Incidence in the male population were greater than incidence in the female population.During the study period,esophageal cancer incidence among the total population,the male population and the female population rose from 2001 to around 2011 and then declined during the recent few years.2.The study discovered a trend of gradient rising from northeast to southwest in esophageal cancer incidence.The distribution of esophageal cancer incidence is significantly heterogeneous at village level and significant high incidence and low incidence clusters were found,which indicated that geographical factors may have influence on the high incidence of esophageal cancer.3.The high incidence clusters and low incidence clusters in Feicheng city showed different epidemiological characteristics.The proportion of male cases in high incidence clusters was greater than that in low incidence clusters.4.Altitude,cinnamon soil,nitrate nitrogen in water and pH in water were factors associated with the high incidence of esophageal cancer.Negative association between altitude and high esophageal cancer incidence was found while positive associations were found in cinnamon soil,nitrate nitrogen in water and pH in water. |
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