Cluster of brain cancers spuriously suggesting occupational risk among glassworkers.

Indications of an increased risk of brain cancer in some, but not all, epidemiologic studies on glassworkers inspired further investigations in a geographically restricted region where the Swedish glass industry is located. Only a small and insignificant excess of brain cancer death was found among glassworkers when compared with the rest of the population in the area. However, when the brain cancer mortality of the glassworkers was compared with that of the whole Swedish population, a rather high risk was found, but an equally high risk was also seen for the rest of the population in this region when compared with national figures. Besides glassworkers, especially farmers, but also other occupational groups had an increased risk of brain cancer that suggested the possibility of an environmental factor affecting the whole population in the region. Hence particular worker groups may sometimes take on a regional mortality pattern that simulates an occupational risk.