Background: The aim of this study is to examine the association of urinary cesium with breast cancer risk.Materials and Methods: We collected survey data and urine specimens from 240 women with incident invasivebreast cancer before their treatment and 246 age-matched female controls between October 2009 and July2010. Urinary concentrations of cesium were determined by inductively coupled plasma mass spectrometry.Interviews were conducted by face-to-face to obtain information on potential breast cancer risk factors. Logisticregression analysis was used to estimate the associations. Results: Creatinine-adjusted levels [median (25th, 75th)ug/g] of cesium in cases and controls were 17.6 (13.1, 24.0) and 19.3 (15.3, 25.7), respectively. After adjustmentfor potential risk factors, women in the second and highest tertile of cesium showed a decreased risk of breastcancer in a dose-dependent manner as compared with those in the lowest tertile [ORs and 95% CIs: 0.75 (0.46-1.22) and 0.50 (0.30-0.82), respectively]. This decrease was more evident in women with ER positive or localizedclinical stage in an exploratory stratification analysis. Conclusions: These findings suggest that cesium may haveanticancer efficacy and urinary cesium has potential as a biomarker for breast cancer risk assessment.
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