Contact with ruminants is associated with esophageal squamous cell carcinoma risk

The etiology of esophageal squamous cell carcinoma (ESCC) in the high risk area of northern Iran is only partially known. We aimed to investigate prolonged animal contact as a risk factor for ESCC in this population. From 2003 to 2007, we administered a validated questionnaire to 300 ESCC cases and 571 randomly selected controls matched for neighborhood of residence, age (±2 years) and sex. Questions on lifelong exposure to equines, ruminants, canines, and poultry, including duration and level of contact, were asked in a face-to-face interviews. Conditional logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs) adjusted for potential confounders. A total of 94.7% of cases and 68.7% of controls reported lifelong history of contact with ruminants. After controlling for potential confounders, contact with ruminants was associated with an eightfold increase (95% CI: 3.92-14.86) in risk of ESCC, and increments in duration of contact raised the risk estimates in a dose-dependent manner. Contact with equines and poultry did not significantly change associated OR for ESCC risk and contact with ruminants. OR (95% CI) for contact with canines was 1.99 (1.35-2.93) which after exclusion of contact with ruminants was not significant (OR for contact only with canine: 3.18, 95% CI: 0.73-13.17). These results add to the evidence that contact with ruminants may increase the risk of ESCC.