Familial Risks of Esophageal Cancer in the Caspian Littoral of Iran

In northeastern Iran there is an area of high incidence of esophageal cancer which is populated by residents of Turkmen ancestry. Several environmental risk factors for esophageal cancer have been proposed, but the roles of familial and genetic factors have not been studied extensively in the Turkmen population. We evaluated the importance of familial risk factors for esophageal cancer by performing a case-control study of 167 cases of esophageal squamous cell carcinoma and 200 controls of Turkmen ethnicity. Detailed family pedigrees of the cases and controls were constructed, which documented all cancers in first- and seconddegree relatives. The actuarial risk of cancer was then estimated in 2097 first-degree relatives of cases and 2783 first-degree relatives of the controls. A hazard ratio was constructed, based on a comparison of the two cumulative incidence curves. The risk to age 75 of esophageal cancer in the first-degree relatives of Turkmen patients with esophageal cancer was 34%, versus 14% for the first-degree relatives of the controls (hazard ratio = 2.3; p = 3 x 10-8). 9.6% of the cases reported that their parents were related, versus 2.5% of the controls (odds ratio = 4.1; p -value = 0.006). Familial factors are important in the etiology of esophageal cancer among the Turkmen residents of Iran. The hazard ratio of 2.3 for cancer among first-degree relatives is consistent with an important contribution of heritable factors. It will be of interest to perform marker studies to establish which genes are responsible.