Environmental cadmium as a potential risk factor for thyroid cancer
Authors: John Kovach, Maisie Shindo, Sharon Liang, Jingxuan Liu, Joy Roelfs, John Chen, David Bellis, Patrick Parsons
Journal: Cancer Research (2008)

5593  We measured cadmium (Cd) in normal thyroid tissue of thyroid cancer (TC) patients to determine if Cd is present at levels that might enhance mutagenesis. We hypothesize that environmental Cd contributes to increased risk of TC. Although an increase in TC has been attributed to improved diagnosis (ultrasound vs. palpation), there appears to be a real increase in incidence. In NY State, from1994-2004, there was a near doubling of TC incidence in men and a doubling in women. Cd, a ubiquitous environmental pollutant, has been linked to increased risk of several diseases including lung cancer and, recently, breast cancer (McElroy et al, JNCI 98:869-873, 2006). Among its toxic effects, Cd disrupts thyroid and other endocrine functions and inhibits DNA repair, especially base excision (BER). Cd pollution is increasing worldwide with a ten-fold increase in Cd in mammalian bones in the 20 th century (Jawaroski et al, Sci Total Env 43:103-126, 1985). With an in vivo half-life of 30 years, Cd is known to accumulate in the liver and kidney of non-smoking, non-occupationally exposed individuals and wildlife such as moose and deer. Cd has not been measured in many other tissues in which common cancers arise. Suffolk County, NY (SCNY) has a long history of potato farming, which requires extensive use of phosphate fertilizers that frequently contain Cd. Copper and lead (PB)arsenicals were also used for decades to control potato blight. Both arsenic (As) and Pb may enhance Cd toxicities including inhibition of DNA repair. Although data on Cd levels in SCNY farmland are lacking, soil samples from 10 potato fields in SCNY had 12 to 24 fold more As and 2-4 fold more Pb than a never cultivated field (Sanok et al, Chemosphere 30: 803-806, 1995). Residents of SCNY have high rates of female breast cancer (142.7) and thyroid cancer (16.9 and 7.1 for women and men, respectively) (cases/100,000 persons age-adjusted to the 2000 US population). We measured Cd in normal tissue from thyroids containing a papillary carcinoma from 6 non-occupationally exposed residents of SCNY, 4 women (ages 36, 38, 39, and 70) and 2 men (ages 42 and 61). Each tissue sample was freeze dried, weighed, digested in nitric acid with microwave assisted heating, and analyzed for Cd by Inductively Coupled Plasma-Mass Spectrometry. Cd was detected in all samples ranging from 0.285 to 1.250 ug/g dry weight (average of two samples from each gland). These values correspond to 0.51 to 2.23 umoles/g wet weight, concentrations compatible with inhibition of BER and potentially, other mechanisms of DNA repair. We recommend, therefore, studying the potential role of Cd as a contributor to increased risk of TC in SCNY. Next steps are to measure Cd levels in thyroid tissue from additional TC patients and patients with benign thyroid disease and to determine if residents of SCNY have increased total body burdens of Cd (as measued by urinary Cd) compared to the average US resident as reported in the National Exposure Report issued by the CDC.