IJE Advance Access published online on May 4, 2009
International Journal of Epidemiology, doi:10.1093/ije/dyp195
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Socio-economic status and oesophageal cancer: results from a population-based case–control study in a high-risk area
1Digestive Disease Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
2International Agency for Research on Cancer, Lyon, France.
3King's College London, Thames Cancer Registry, London, UK.
4Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA.
5Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden.
6Golestan Research Center of Gastroenterology and Hepatology, Golestan University of Medical Sciences, Gorgan, Iran.
7Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
8Department of Statistics, University of Washington, Seattle, WA, USA.
*Corresponding author. International Agency for Research on Cancer, 150 cours Albert Thomas, 69008 Lyon, France. E-mail: boffetta{at}iarc.fr Digestive Disease Research Center, Tehran University of Medical Sciences, Shariati Hospital, Kargar Shomali Avenue, 14117 Tehran, Iran. E-mail: malek{at}ams.ac.ir
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Abstract |
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Background Cancer registries in the 1970s showed that parts of Golestan Province in Iran had the highest rate of oesophageal squamous cell carcinoma (OSCC) in the world. More recent studies have shown that while rates are still high, they are approximately half of what they were before, which might be attributable to improved socio-economic status (SES) and living conditions in this area. We examined a wide range of SES indicators to investigate the association between different SES components and risk of OSCC in the region.
Methods Data were obtained from a population-based case–control study conducted between 2003 and 2007 with 300 histologically proven OSCC cases and 571 matched neighbourhood controls. We used conditional logistic regression to compare cases and controls for individual SES indicators, for a composite wealth score constructed using multiple correspondence analysis, and for factors obtained from factors analysis.
Results We found that various dimensions of SES, such as education, wealth and being married were all inversely related to OSCC. The strongest inverse association was found with education. Compared with no education, the adjusted odds ratios (95% confidence intervals) for primary education and high school or beyond were 0.52 (0.27–0.98) and 0.20 (0.06–0.65), respectively.
Conclusions The strong association of SES with OSCC after adjustment for known risk factors implies the presence of yet unidentified risk factors that are correlated with our SES measures; identification of these factors could be the target of future studies. Our results also emphasize the importance of using multiple SES measures in epidemiological studies.
Keywords Oesophageal cancer, socio-economic status, case–control, epidemiology, Iran, factor analysis, correspondence analysis
Accepted 24 March 2009