Background:The current study followed-up site-specific cancer risks in an unique cohort with 30 years’ follow-up after long-term low-dose-rate radiation exposure in Taiwan.Methods:Six thousand two hundred and forty two Taiwanese people received extra exposure in residential and school buildings constructed with Co-60-contaminated steel from 1982 until informed and relocated in early 1990s. The additional doses received have been estimated. During 1983–2012, 300 cancer cases were identified through the national cancer registry in Taiwan, 247 cases with minimum latent periods from initial exposure. The hazard ratios (HR) of site-specific cancers were estimated with additional cumulative exposure estimated individually.Results:Dose-dependent risks were statistically significantly increased for leukaemia excluding chronic lymphocytic leukaemia (HR100mSv 1.18; 90% CI 1.04–1.28), breast cancers (HR100mSv 1.11; 90% CI 1.05–1.20), and all cancers (HR100mSv 1.05; 90% CI 1.0–1.08, P=0.04). Women with an initial age of exposure lower than 20 were shown with dose response increase in breast cancers risks (HR100mSv 1.38; 90% CI 1.14–1.60; P=0.0008).Conclusions:Radiation exposure before age 20 was associated with a significantly increased risk of breast cancer at much lower radiation exposure than observed previously.

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