Cancer mortality among Chinese migrants: a review.

BACKGROUND: Epidemiological studies of cancer among migrant groups are beneficial in that they can provide insight into genetic and environmental factors in disease aetiology. Seven studies in the epidemiological literature have examined cancer mortality in migrants from China; methodological features and findings, which display remarkable consistencies between studies, are reviewed here.
METHODS: Papers were included that compare site-specific cancer mortality patterns in first and second generation migrants to the experience in the host regions using vital statistics and census data. Rates had to be standardized either indirectly (using age-specific rates from the host regions) or directly (using a standard age structure) and standardized mortality ratios (SMR) or rate ratios (RR) were calculated.
RESULTS: Migrant males had overall mortality from cancer that was often in significant excess compared to the host experience; results for females (for overall cancer) were equivocal. Both sexes had large and significant excess mortality from nasopharyngeal and liver cancer; SMR and RR were also consistently elevated for cancers of the stomach and oesophagus. There was notable attenuation in the high risk at these four sites in the second generation. All studies reported pronounced and significant reduced risk for prostatic cancer and female breast cancer, with little or no increase in mortality in the second generation. The SMR and RR also tended to be below unity for brain, bladder and kidney cancer.
CONCLUSIONS: The results of this review indicate that cancer risk at several sites among Chinese migrants appears to be in transition, and that these findings are consistent across studies.