Brain tumour mortality in immigrants.

All Canadian deaths due to malignant brain tumour for the years 1970-73 were identified and analysed for country of birth. The years 1970-73 were chosen since in later years country of birth was no longer available for each death. The brain tumour population consisted of 1551 male and 1058 female deaths and matched controls were chosen from deaths due to other causes. Americans who died of brain tumour in Canada had a standardized mortality ratio (SMR) of 1.0 compared to their fellow Americans in the USA. Italian, German, Dutch and British immigrants had SMR between 1.5 and 2.6 compared to rates in their home countries and between 1.24 and 2.09 when compared to Canadian rates. A series of graphs shows the increased risk for male immigrants quite dramatically, and indicates that for females the increases were less pronounced. Further analysis showed that the excess risk is confined to those who were born in Western Europe while their Canadian-born children experienced the same rates as all Canadians. Based on the limited information available, occupation could not be shown to play a role in establishing risk. An attempt was made to pinpoint the years of immigration which showed the greatest risk. It is concluded that the determination of risk of brain tumour has a strong environmental component. The possibilities for identification of this component are discussed.