基金志谢: We thank the staff of the Atrak Clinic, including Karim Aghcheli, Noushin Taghavi, Haji-Amin Marjani, Rabaeh Rajabzadeh, Monireh Badakhshan, Bita Mohammadi, Halimeh Eskandamejhad, Safora Kor, Soleiman Kasalkheh, and Ashor Yolmeh Noorli Radgohar, Abdolazim Khozeini, Rahmat Ghaziani, Mohammad Hasan Brazandeh, Abdolhakim Ebadati, Naser Keramat, and Ahmad Nosrati for their valuable help +2 种基金 the local health networks and health workers (Behvarzes) in the study area for their assistance in recruitment of controls the Iranian Social Security Organization for their local support and the Golestan Cohort Study Center staff for their dedicated work. 关于作者( Contributors): See bmj. com. 基金( Funding): This study was supported by the Digestive Disease Research Center of Tehran University of Medical Sciences ( grant No 82-603), by an intramural programme of the National Cancer Institute, National Institutes of Health, and by the International Agency for Research on Cancer, The funding sources had no role in the design, conduct, statistical analysis and interpretation of results, or writing of the manuscript. 利益竞争(Competing interests): None declared. 伦理学批准 (Ethical approval): The ease-control study was reviewed and approved by the institutional review boards of the Digestive Disease Research Center (DDRC) of Tehran University of Medical Sciences and the US National Cancer Institute. Both cases and controls gave written informed consent for the interview. The conduct of Golestan Cohort Study was reviewed and approved by the institutional review boards of DDRC, the International Agency for Research on Cancer, and the US National Cancer Institute.