Background: Radiation-related heart disease and lung cancer can occur following radiotherapy for breast cancer but the duration of any mortality risk is uncertain.
Methods: Mortality ratios, by laterality of breast cancer, were estimated using Poisson regression for 558 871 women recorded with breast cancer during 1973-2008 in the Surveillance, Epidemiology and End Results (SEER) cancer registries and followed until 01 January 2009.
Results: For women diagnosed with breast cancer during 1973-1982 and given radiotherapy shortly afterwards, the cardiac mortality ratios, left-sided vs right-sided, were 1.19 (1.03-1.38), 1.35 (1.05-1.73), 1.64 (1.26-2.14) and 1.90 (1.52-2.37) at <10, 10-14, 15-19 and 20+ years since diagnosis (2p for trend: <0.001). The lung cancer mortality ratios, ipsilateral vs contralateral, in these women were 1.05 (0.57-1.94), 2.04 (1.28-3.23) and 3.87 (2.19-6.82) at <10, 10-19 and 20+ years, respectively, (2p for trend: 0.002). For women irradiated during 1983-92 there was evidence of radiation-related mortality for lung cancer, but not for heart disease. For women irradiated since 1993 there is, as yet, little evidence of any radiation-related mortality.
Conclusion: In this population, the radiation-related risks were larger in the third decade after exposure than during the first two decades.