COHORT PROFILE Cohort Profile: The Golestan Cohort Study— a prospective study of oesophageal cancer in northern Iran

The earliest reports of high incidence of oesophageal cancer (OC) in the northern parts of Iran date back to the early 1970s. A population-based cancer registry was established in 1969 as a joint effort between Tehran University and the International Agency for Research on Cancer (IARC). This registry confirmed the high incidence of OC in the eastern portion of the Caspian Sea littoral, in the area that is now known as Golestan Province. The highest incidence rates were reported from the semi-desert plain settled mainly by people of Turkmen ethnicity in Gonbad and Kalaleh counties, with estimated incidence rates of 109/10 among men and 174/10 among women (adjusted to the 1970 World Standard Population). The registry also showed low incidence of OC in the nearby Gilan province, 300 km to the west of Golestan, with incidence rates of 15/10 and 5.5/10 among men and women, respectively. A series of studies were conducted in the region in the 1970s, but they were not conclusive in explaining the very high rates. However, they pointed to several factors, including: (i) a diet deficient in fruits and vegetables; (ii) low socio-economic status; (iii) thermal injury from consumption of very hot tea; and (iv) carcinogen exposure from lifestyle factors including opium consumption. The high incidence of OC in Golestan was confirmed by a recent screening study. Aetiological hypotheses related to diet and life style can be best addressed in prospective cohort studies, in which measurement error can be reduced and recall bias is minimal. From 2002 to 2003, a pilot study of 1057 subjects was conducted by the Digestive Disease Research Center (DDRC) of Tehran University of Medical Sciences in collaboration with IARC and the US National Cancer Institute (NCI) to evaluate the logistics of establishing a prospective study in Golestan. The aims of the pilot study were to assess the response rate of the study population, to develop valid and reliable methods for assessing nutritional, anthropometric and life-style factors, to develop follow-up methods to ascertain mortality and cancer incidence among the enrolled subjects, and to establish efficient procedures for collecting and storing biological samples. Results of the pilot study confirmed the feasibility of conducting a prospective cohort study in Golestan. Subsequently, the Golestan Cohort Study (GCS) was launched in January 2004. This study is part of a series of investigations into the etiology of upper gastrointestinal cancers in this area, collectively named Gastric and Oesophageal Malignancies in Northern Iran (GEMINI). The study protocol and the informed consent used for this study were approved by the ethical review committees of DDRC, IARC and NCI. In June 2008, the accrual goal of 50 000 subjects was reached and enrollment was closed. * Corresponding author. Lifestyle, Environment and Cancer Group, International Agency for Research on Cancer, Lyon, France. E-mail: [email protected] or Digestive Disease Research Center, Tehran University of Medical Sciences, Tehran, Iran. E-mail: [email protected] 1 Digestive Disease Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2 International Agency for Research on Cancer, Lyon, France. 3 Golestan Research Center of Gastroenterology and Hepatology, Golestan University of Medical Sciences, Gorgan, Iran. 4 Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA. 5 University of Cambridge, Cambridge, UK. Published by Oxford University Press on behalf of the International Epidemiological Association