Dose-Response Relationship between Inorganic Arsenic Exposure and Lung Cancer among Arseniasis Residents with Low Methylation Capacity.

Background: Exposure to inorganic arsenic (InAs) has been documented as a risk factor for lung cancer. This study examined the association between InAs exposure, its metabolism, and lung cancer occurrence.
Methods: We followed 1,300 residents from an arseniasis area in Taiwan, determined urinary InAs metabolites, and identified 39 lung cancer cases. Cox proportional hazards model was performed.
Results: The results demonstrated that participants with either the primary methylation index [monomethylarsonic acid (MMA)/InAs] or the secondary methylation index [dimethylarsenic acid (DMA)/MMA] lower than their respective median values were at a higher risk of lung cancer (HRs from 3.41 to 4.66) than those with high methylation capacity. The incidence density of lung cancer increased from 79.9/100,000 (year-1) to 467.4/100,000 (year-1) for residents with low methylation capacity and from 0 to 158.5/100,000 (year-1) for residents with high methylation capacity when the arsenic exposure dose increased from 2 to 10 ppb to ≥200 ppb, respectively. The analyses revealed a dose-response relationship between lung cancer occurrence and increasing arsenic concentrations in drinking water as well as cumulative arsenic exposure (monotonic trend test; P < 0.05 and P < 0.05, respectively) among the residents with low methylation capacity. The relationship between arsenic exposure and lung cancer among high methylators was not statistically significant.Conclusions: Hypomethylation responses to InAs exposure may dose dependently increase lung cancer occurrence.Impact: The high-risk characteristics observed among those exposed should be considered in future preventive medicine and research on arsenic carcinogenesis. Cancer Epidemiol Biomarkers Prev; 26(5); 756-61. ©2016 AACR. ©2016 American Association for Cancer Research.