Genetics and Human Mesothelioma

Abstract

In the villages of Karain (population 600) and Tuzkoy (population 1400) in Cappadocia, a region in Central Anatolia, Turkey, characterized by volcanic tuffs and natural caves, 50% or more of deaths are caused by malignant mesothelioma. These two villages, like most other villages in the region, were built with stones mined from the nearby natural caves. Dr. Y.I. Barish discovered this unique very high incidence of mesothelioma (1). Soon after, scientists looked for asbestos, which in the 1970s was the only known causative factor for mesothelioma. Some asbestos was found (2), but subsequent studies demonstrated that in Cappadocia low asbestos amounts are found almost everywhere because it is a natural component of that volcanic terrain and because asbestos-based stucco (containing tremolite asbestos) has been widely used in building construction (3). It appeared that asbestos could not account for the unique high incidence of mesotheliomas in these two villages (4). Another type of mineral fiber, erionite, which had been detected in the lungs of several villagers, was suspected as a causative agent (1,4). Erionite is a type of fibrous zeolite commonly found in the stones of the houses of Karain and Tuzkoy. When erionite was injected intrapleurally into animals, it caused mesothelioma, and it was concluded that erionite was the cause of mesothelioma in these villages (5). Erionite, therefore, appeared much more potent than asbestos in causing mesothelioma because more than half of the villagers died of this disease. Erionite was claimed to be the most potent chemical human carcinogen (6). Studies tried to link erionite to other human tumors, but except for mesotheliomas there is no significant difference in the incidence of any other tumor types in these two villages compared with the rest of Turkey (7). Why such a potent carcinogen would specifically cause mesothelioma was unknown. Why about 50% of villagers appeared to suffer no consequence from exposure to such a potent carcinogen was also unknown. During repeated visits to these villages, we suspected that erionite was not the only cause of mesothelioma. In the villages of Karain and Tuzkoy, mesothelioma developed mostly in certain houses, called the