Increased cancer mortality in Taiwanese inter-island migrants.

Higher mortality due to various forms of cancer was observed in emigrants, who had moved from the isolated and impoverished Taiwanese island of Matsu to the more affluent main island. A total of 13,691 ethnic Matsunese aged 30 years and above were enrolled in a study comparing cumulative and standardised mortality rates between emigrants to the main island of Taiwan and those who stayed behind. Poisson regression modelling was used to analyse the effects of migration. For all causes of mortality, the adjusted relative risk was 1.24 with a confidence interval (CI) at the 95% level of 1.08-1.42 for emigrants compared to Matsunese non-emigrants. Deaths from cancer and diabetes in emigrants showed similar results, i.e. an adjusted relative risk of 1.25 (95% CI, 1.00-1.57) and 1.93 (95% CI, 1.20-3.11), respectively. Higher cumulative incidence rates for all cancers and the three leading cancer forms (hepatocellular carcinoma, gastric cancer and lung cancer) in emigrants were also observed. However, no significant difference in the survival time of most of the cancer forms was noted between the two groups. The finding that moving to a more affluent area paradoxically leads to incidence of cancer and higher mortality might be explained by adoption of various forms of unhealthy behaviour, psycho-social factors and the general risks related to life in urbanized environments.