Occupational arsenic exposure and digestive and head and neck cancers: a systematic review and meta-analysis.

Arsenic is a known carcinogen for the lungs, the bladder, and the skin, while systematic evidence on other cancer types is lacking, especially for occupational exposure. Thus, we aimed to systematically summarize current evidence on the association between occupational arsenic exposure and digestive cancers, including head and neck cancer (HNC). We conducted a systematic review on Pubmed, Web of Science, and Embase search engines. We computed pooled relative risks (RRs) and corresponding 95% confidence intervals (CIs) using DerSimonian and Laird random-effects model. Occurrence of publication bias was assessed using contour-enhanced funnel plots and Egger's test. Twenty-two studies on digestive cancers and 11 on HNC were included in the meta-analysis. RRs for the association with occupational exposure to arsenic of 1.23 (95% CI: 1.07-1.40; I2=72.3%, p<0.001) and 1.08 (95% CI: 0.76-1.53; I2=76.6%, p<0.001) for digestive cancer and HNC, respectively, were observed. As for specific cancer types, arsenic was associated with rectal cancer (RR: 1.51; 95% CI: 1.003-2.28; I2=37.0%, p=0.174), but not with other investigated cancer types. No clear evidence of publication bias was found. The results of our study suggest that the observed association between occupational arsenic exposure and digestive cancer might be mainly driven by a positive association for rectal cancer, while arsenic exposure did not appear to be associated with HNC. However, further high-quality studies with detailed assessment of arsenic exposure are warranted to clarify the potential association of arsenic with digestive cancers and HNC.

The role of chance in cancer causation.

In the last years, the discussion about the role of chance in the causation of cancer has generated much scientific and public debate. The concept that chance, or "bad luck", as responsible for a majority of the variation of cancer incidence, may be misleading, possibly causing an underestimation of the role played by known risk factors. In this commentary we discuss how host and external factors interact with chance in cancer causation in different ways, and provide examples of situations where chance appears to play only a minor role on cancer onset.