Persistent and emerging cancer risks after migration: Evidence from North and South Korean cohorts.

[BACKGROUND] North Korean defectors in South Korea offer a rare natural model to trace cancer risk evolution after rapid environmental transition, given shared genetics but markedly contrasting early life exposures with South Korean residents.

[METHODS] Using the Korean National Health Insurance database, we constructed a nationwide matched cohort of 25,798 North Korean defectors and 1,276,601 South Korean residents (1:50 frequency matching by sex, age, and index year). We compared overall and site-specific cancer risks and examined time-varying hazard ratios (HRs) since resettlement.

[RESULTS] Overall cancer risk was higher among defectors (HR 1.13; 95% confidence interval, 1.07-1.18), particularly in men (HR 1.31). Liver (HR 2.53), uterine cervical (HR 2.10), and lung cancer (HR 1.69) were markedly elevated, reflecting infection- and deprivation-related legacies. In contrast, cancers more prevalent in developed countries, notably breast (HR 0.48) and colorectal (HR 0.71), were initially lower. However, HRs began to rise over time, especially for breast cancer, indicating a trend toward convergence with host-population patterns.

[CONCLUSION] The cancer profile of North Korean defectors demonstrates a dual burden: persistent risks from infection-related cancers rooted in pre-defection exposures and growing vulnerability to lifestyle-related cancers after resettlement. These findings highlight the importance of dual-track prevention strategies that address both legacy and emerging cancer risks in rapidly transitioning populations.