30 years follow-up and increased risks of breast cancer and leukaemia after long-term low-dose-rate radiation exposure.

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 (HR 1.18; 90% CI 1.04-1.28), breast cancers (HR 1.11; 90% CI 1.05-1.20), and all cancers (HR 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 (HR 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.