News www.thelancet.com/oncology Vol 18 May 2017 581 Carcinogenicity of welding, molybdenum trioxide, and indium tin oxide In March 2017, 17 scientists from ten countries met at the International Agency for Research on Cancer (IARC; Lyon, France) to evaluate the carcinogenicity of welding, molybdenum trioxide, and indium tin oxide. These assessments will be published in volume 118 of the IARC Monographs. 1 Worldwide, an estimated 11 million workers have a job title of welder, and around 110 million additional workers probably incur welding- related exposures. Welding can involve exposures to fumes, gases, radiation (ultraviolet [UV] radiation and electromagnetic fields) and co- exposures to asbestos and solvents. Welding involves several processes (eg, oxyfuel [gas], arc, and resistance welding) and materials (eg, mild and stainless steel). Exposure determinants include the process, material welded, ventilation, degree of enclosure, and use of personal protection. The carcinogenicity of welding fumes was assessed by IARC in 1989 2 and classified as “possibly carcinogenic to humans” (Group 2B), based on ‘‘limited evidence in human beings’’ and ‘‘inadequate evidence’’ in experimental animals. 3 UV radiation was classified in Group 1 in volume 100D of the IARC Monographs. Substantial new evidence has since accumulated from observational and experimental studies. In the present evaluation, welding fumes and UV radiation from welding were classified as “carcinogenic to humans” (Group 1). Arc welding generates UV radiation, a risk factor for the rare cancer ocular melanoma. Various ocular disorders (eg, cataracts or keratoconjunctivis) occur in both welders and nearby workers. Sufficient evidence for the carcinogenicity of UV radiation from welding came from eight partly overlapping case–control studies and two census-based cohort studies that reported on ocular melanoma. Most case–control studies showed positive associations, with risks of developing ocular melanoma generally increased by between two-fold and ten-fold. Two of three studies that assessed risk by duration of employment as a welder showed positive trends. 3,4 These studies also showed increased ocular melanoma risk associated with eye burns—a proxy for UV exposure— and one reported a positive exposure– response association for cumulative occupational exposure to artificial UV radiation, including welding. 3,4 Risks persisted after adjustment for sun exposure, sun bed use, or both. 4–6 Welding fumes are produced when metals heated above their melting point vaporise and condense to fine particles (mostly <1 μm in size). Most studies, including more than 20 case–control studies and nearly 30 occupational or population-based cohort studies, reported increased risks of lung cancer in welders or other workers exposed to welding fumes. Exposure–response associations with indices of longer or greater cumulative exposure to welding fumes were also reported in several studies, some of which were large, high-quality studies. 7–10 Exposure to fumes was assessed indirectly through welding process or material, branch of industry, job title, expert assessment, or self-report. Asbestos exposure and tobacco smoking, which are important potential confounders, could not explain the observed excess lung cancer risk in welders. Positive associations persisted after adjusting directly or indirectly for smoking, asbestos co-exposure, or both; 7–10 restricting to non-smokers or low- level smokers; 11 and in cohorts with low or minimal asbestos exposure. 12 Positive associations for occupation as a welder and kidney cancer were reported in nearly all relevant cohort and case–control studies. However, few studies adjusted for solvents used for cleaning metal in tandem with welding, such as trichloroethylene (a risk factor for kidney cancer). Increased risks were consistently reported across countries, occupational settings, and study designs. However, chance, bias, and confounding could not be reasonably ruled out because some findings were not statistically significant, several studies had few exposed cases, and there was little evidence of an exposure–response association. For all other cancers, the evidence for carcinogenicity was inadequate because of inconsistent findings across studies, insufficient numbers of studies, or the potential for confounding or selection bias. The Working Group concluded that there is ‘‘sufficient evidence in humans’’ that welding fumes cause lung cancer and limited evidence for kidney cancer. There is limited evidence in experi- mental animals for the carcinogenicity of gas metal arc–stainless steel welding fumes. In one oropharyngeal aspiration study and one inhalation study in male A/J mice, gas metal arc–stainless steel welding fumes promoted 3-methylcholanthrene- induced lung tumours. 13,14 Absorption and excretion of metals (chromium, nickel, and manganese) was shown in people exposed to welding fumes, but data for particle deposition and clearance in welders were scarce. Strong evidence suggests that welding fumes induce chronic inflammation and are immunosuppressive. Lung and systemic inflammation biomarkers were increased in many panel studies (of cross-sectional and cohort design) of various arc welding fumes. 15 Risk for infection (pneumonia) was increased Published Online April 10, 2017 http://dx.doi.org/10.1016/ S1470-2045(17)30255-3 For more on the IARC Monographs see http://monographs.iarc.fr/ Upcoming meetings June 6–13, 2017, Volume 119: Some chemicals in food and consumer products Oct 10–17, 2017, Volume 120: Benzene IARC Monograph Working Group Members J Hansen (Denmark)—Meeting Chair; A K Nersesyan (Austria); J Lavoué (Canada); D Luce (France); W Ahrens (Germany); S Fukushima (Japan); H Kromhout, S Peters (Netherlands); A ‘t Mannetje (New Zealand); M Albin (Sweden); M G Baker, D C Christiani, J M Fritz, W M Gwinn, R M Lunn, E J Tokar, P C Zeidler-Erdely (USA) Declaration of interests SP declares that her previous research unit at the University of Western Australia received research support (ceased July, 2014) from WesTrac Ltd (Western Australia, Australia)— a construction equipment supplier—to investigate the adverse health effects of environmental asbestos exposure. All other working group members declare no competing interests. Invited Specialists None Representatives and WHO staff Y Chen, for the Health and Safety Executive (HSE), UK; P Guillou, for the French Agency for Food, Environmental and Occupational Health and Safety (ANSES), France; F Pega, for WHO, Geneva, Switzerland; A Ullrich, for WHO, Geneva, Switzerland TLO_May17_News_IARC DOI: S1470-2045(17)30255-3 Embargo: April 10 2017; 23:30 GMT