Spatial Analysis of Esophageal Cancer Mortality in a High-risk Population in China: Consistent Clustering Pattern in 1970-74 and 2011-13

Purpose: Almost half of the global esophageal cancer (EC) deaths occurred in China. This study aims to examine the geographic spread of EC mortality in two periods in a large Chinese population. Methods: Age-standardized mortality rates (ASMRs) for 140 county-level units in Shandong Province during the periods 1970-74 and 2011-13 were derived using data from the First National Cause-of-Death Survey and the Shandong Death Registration System, respectively. ASMRs were smoothed using Area-to-Area Poisson kriging technique. Spatial scan statistics were used to detect spatial clusters with higher EC mortality and clusters with greater temporal changes in EC mortality. Results: The provincial average ASMR decreased from 13.0 per 100,000 in 1970-74 to 5.8 in 2010-13. Almost all counties or districts have experienced a decrease in EC mortality, while the reduction was particularly pronounced in the mid-west region. This study has identified a geographical cluster with much higher EC mortality rates and the clustering pattern has largely unchanged over the past 40 years. Residents living in the cluster during 1970-74 were 2.7 (95% CI: 2.2-3.4) times more likely to die from EC than the rest of the province. The corresponding risk ratio for the 2011-13 cluster was 3.7 (95% CI: 2.8-5.0). Conclusions: This study detected a geographically defined subpopulation in Shandong, China with much higher risk of dying from EC. This spatial pattern has been consistent over the past few decades. The results suggest the key drives for geographic variations in esophageal cancer may not have changed.