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Upper gastrointestinal (UGI) cancer, including esophageal and gastric, is one of the most common cancers in the world. Hence, the determination of risk factors of UGI helps to reduce the economic and social burden of this cancer in communities. In Iran, the consumption of opium because of its neighborhood with Afghanistan are considerable. In this study, we examine the causal effect of opium use on the time to UGI cancer death. Based on the Golestan Cohort Study (GCS) in northeastern of Iran, about 50000 adults were enrolled to the study for four years (2004-2008) and followed annually until July 2018. We used "parametric g-formula" to study the causal effect of opium use on the time to death due to UGI. In this study, the information of 49946 individuals due to missingness were analyzed. So the median of follow-up time was 144 months and the prevalence of opium use was 17% (about 8489 persons). During the follow-up period, 593 (1.2%) death from upper gastrointestinal cancer were reported. The study showed that the effect of opium use on the time to UGI death was statistically significant (adjusted risk-ratio based on parametric g-formula = 1.31, 95% CI: [1.04, 1.65]). Additionally, the Population Attributable Fraction (PAF) in UGI cancer deaths of opium use was estimated 5.3% (95% CI: [0.6%, 11.3%]). Our results showed a causal effect of opium use on the intensity of upper gastrointestinal cancer death., Competing Interests: The authors have read the journal's policy and the authors of this manuscript have the following competing interests: AS is a paid employee of No Way New Way Company. There are no patents, products in development or marketed products associated with this research to declare. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Background: Control selection is a major challenge in epidemiologic case-control studies. The aim of our study was to evaluate using hospital versus neighborhood control groups in studying risk factors of esophageal squamous cell carcinoma (ESCC)., Methodology/principal Findings: We compared the results of two different case-control studies of ESCC conducted in the same region by a single research group. Case definition and enrollment were the same in the two studies, but control selection differed. In the first study, we selected two age- and sex-matched controls from inpatient subjects in hospitals, while for the second we selected two age- and sex-matched controls from each subject's neighborhood of residence. We used the test of heterogeneity to compare the results of the two studies. We found no significant differences in exposure data for tobacco-related variables such as cigarette smoking, chewing Nass (a tobacco product) and hookah (water pipe) usage, but the frequency of opium usage was significantly different between hospital and neighborhood controls. Consequently, the inference drawn for the association between ESCC and tobacco use did not differ between the studies, but it did for opium use. In the study using neighborhood controls, opium use was associated with a significantly increased risk of ESCC (adjusted OR 1.77, 95% CI 1.17-2.68), while in the study using hospital controls, this was not the case (OR 1.09, 95% CI 0.63-1.87). Comparing the prevalence of opium consumption in the two control groups and a cohort enrolled from the same geographic area suggested that the neighborhood controls were more representative of the study base population for this exposure., Conclusions/significance: Hospital and neighborhood controls did not lead us to the same conclusion for a major hypothesized risk factor for ESCC in this population. Our results show that control group selection is critical in drawing appropriate conclusions in observational studies.

The very high incidence of oesophageal squamous cell carcinoma (ESCC) in Golestan Province in northeastern Iran was suggested by studies in the 1970s as partly due to opium use, which is not uncommon in this area, but based on limited numbers. From December 2003 to June 2007, we administered a validated structured questionnaire to 300 ESCC cases and 571 controls, matched on neighbourhood of residence, age (+/-2 years), and sex. We used conditional logistic regression models to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs) adjusted for potential confounders. Compared with those who used neither tobacco nor opium, risk of ESCC was increased in those who used tobacco only (OR, 95% CI: 1.70, 1.05-2.73), in those who used opium only (2.12, 1.21-3.74), and in those who used both tobacco and opium (2.35, 1.50-3.67). All forms of tobacco use (cigarettes, hookah, and nass) were associated with higher ESCC risk. Similarly, use of both crude opium and other forms of opium were associated with higher risk. Alcohol consumption was seen in only 2% of the cases and 2% of the controls, and was not associated with ESCC risk.

Epidemiologic studies were undertaken on the Caspian littoral of Iran to investigate the geographic distribution of factors that might underlie the signal differences in incidence of cancer of the esophagus. In zones of contrasting incidence and sex ratio, information was obtained on food intake, smoking and drinking patterns (including tea), other personal habits, occupation, economic and agricultural practices, and methods of food storage preservation, and preparation. The diet in the highest incidence area was markedly restricted to bread and tea. The poor quality of the diet itself was thought to have a role in the increased risk of developing esophageal cancer. The use of opium and sesame oil, consumption of sheep's milk and yogurt, the chewing of nass (confined to men), and the use of dyes (confined to women) were also more prevalent in the high incidence areas. Typical dietary items were analyzed for the polycyclic aromatic hydrocarbons, volatile nitrosamines, aflatoxins, nitrates, and nitrites. The results showed no unusual levels of any of the carcinogens tested or geographic differences.

Previous epidemiological studies have indicated an association between the ingestion of opium pyrolysates, dietary deficiencies, and a high incidence of oesophageal cancer in subjects in north-east Iran. Laboratory studies have shown that pyrolysates of opium and particularly of morphine, a major opium alkaloid, are highly mutagenic in bacteria and induce sister-chromatid exchanges in mammalian cells after metabolic activation. We now report the ability of these pyrolysates to transform Syrian hamster embryo cells in culture and present some evidence for their carcinogenicity in mice and hamsters following topical, subcutaneous, intratracheal and intragastric administration. 6 of the most abundant mutagenic compounds present in morphine pyrolysate were isolated and purified by high-performance liquid chromatography and characterized by gas chromatography/mass spectrometry and 1H-Fourier transform nuclear magnetic resonance spectroscopy. These hitherto unknown compounds, all containing a hydroxy-phenanthrene moiety, were identified as: 3-methyl-3H-naphth[1,2-e]indol-10-ol; 1,2-dihydro-3-methyl-3H-naphth[1,2-e]indol-10-ol; 6-methylaminophenanthren-3-ol; 2-methylphenanthro[3,4-d] [1,3]oxazol-10-ol; 2,3-dimethyl-3H-phenanthro[3,4-d]imidazol-10-ol and 2-methyl-3H-phenanthro[3,4-d]imidazol-10-ol. Mutagenicity in Salmonella typhimurium TA98 of these compounds increased in the order listed, the last compound being 35 times more active than benzo[a]pyrene. The mechanisms, by which these mutagens are formed and metabolically activated are discussed.

Substances which are commonly sucked or chewed in two areas where the incidence of oesophageal cancer is high, the Transkei and north-east Iran, were tested in bacterial mutagenicity assays. Pyrolysed substances, opium dross in north-east Iran and tobacco pipe residues in the Transkei, displayed mutagenic activity in Salmonella typhimurium strains TA98 and TA100 in the presence of rat liver microsomes.