Urinary Cadmium Levels, Breast Cancer Risk, and Environmental Tobacco Smoke Exposure

Cadmium, a highly persistent heavy metal, is categorized as a probable human carcinogen by the U.S. Environmental Protection Agency. In our population-based case-control study of Wisconsin women (USA), we interviewed by telephone 246 case women aged 20-69 years and 254 randomly selected similarly aged controls from September 2004 to February 2005. The urine collection kits were carefully designed to minimize trace element contamination during specimen collection and handling in each participant’s home. After returning the samples by postal mail, cadmium was quantified using inductively-coupled plasma mass spectrometry. The participation proportion for those completing the interview was 75 percent for eligible cases and 71 percent for controls in the parent study.

We performed two cadmium exposure analyses--to evaluate breast cancer risk in the case-control population and to evaluate the possible association of environmental tobacco smoke exposure (ETS) in the control population.

Creatinine-adjusted cadmium levels ranged from 0.02 μg/g to 4.55 μg/g for cases (excluding one observation at 30.95 μg/g) and for controls at 0.08 μg/g to 2.64 μg/g. Approximately 60 percent of the controls reported exposure to parental smoking in the home during childhood. For smoking status 12 percent of the control population were current smokers and 26 percent were former smokers. Recent exposure (approximately 2 years prior to the interview) to smoke at work or in the home was rare (10 percent exposed at work and 6 percent exposed at home).

In contrast, participants were more likely to be exposed to ETS in social settings with only 16 percent reporting no recent ETS exposure in social settings. For our analysis of breast cancer risk and urinary cadmium exposure, we observed a two-fold increased breast cancer risk (odds ratio 2.29; 95 percent confidence interval 1.25-4.20) for the highest creatinine-adjusted cadmium category (•0.53 μg/g) compared to the lowest creatinine-adjusted cadmium category (<0.26 μg/g) after adjustment for established breast cancer risk factors (p- trend = 0.01).

In the control population, comparison of least squares means creatinine-adjusted cadmium levels for smoking status of never, former, or current was significantly different between each group (pvalues< 0.003) with current smokers having the highest cadmium level and never smokers having the lowest level. In comparison to control participants who reported no ETS exposures, the least squares means creatinine-adjusted cadmium levels in women exposed as a child to ETS in the home or as an adult in recent home, work or social settings were not different.

For more information, contact:
Jane McElroy, PhD

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