Background An estimated ~110 million workers are exposed to welding fumes worldwide. An IARC working group (WG) re-evaluated the carcinogenicity of welding fumes in 2017, previously classified as possibly carcinogenic to humans (Group 2B) in 1990, based on limited evidence for lung cancer in humans. The WG conducted a meta-analysis of peer-reviewed epidemiologic studies reporting a relative risk for welding (fumes) and lung cancer, accounting for confounding by exposure to asbestos and tobacco smoking.

Methodology After comprehensive searches in PubMed, Web of Science and Google Scholar databases and reference lists of relevant publications, 23 case-control and 36 cohort and nested case-control studies met our inclusion criteria. We attempted to remove overlapping populations for calculating summary-RRs.

Results The summary-RRs were 1.29 (95% CI: 1.24–1.34; I²=47.5%) for “ever” compared with “never” being a welder or being exposed to welding fumes, 1.27 (95% CI: 1.22–1.32; I²=44.7%) among cohort and nested case-control studies, 1.50 (95% CI: 1.34–1.67; I²=39.9%) for case-control studies, 1.09 (95% CI: 0.98–1.20; I²=23%) adjusted for smoking and asbestos exposure, 1.15 (95% CI: 1.02–1.28), among “shipyard welders”, 1.00 (95% CI: 0.84–1.17) among “stainless-steel welders” and 1.31 (95% CI: 1.03–1.60) among “mild steel welders”. The summary-RR was higher for “gas welders” compared to “arc welders”, but not statistically significant. Increased risks were observed over time periods, occupational settings and geographic locations support an evaluation for an increased risk of lung cancer among welders, independent of exposure to asbestos and tobacco smoking.