Objectives Over 110 million workers are worldwide estimated as exposed to welding fumes, including a complex mixture of nano-sized particles with a carcinogenic potential. The aim of the present study is to investigate cancer risks with a special focus on lung cancer in a large group of Danish welders.

Methods In 1986, 5866 welders completed a comprehensive questionnaire on lifetime exposures, including years with different types of welding. Information on employments after baseline (1986) was obtained from the Supplementary Pension Fund. Life-long exposure to welding particles was estimated based on a Danish job-exposure matrix based on p1200 welding specific measurements of welding particles. Based on the unique central person number assigned to all residents in Denmark welders were followed-up for cancer (1987–2015) in the nationwide Danish Cancer Registry. Similarly, information on vital status was obtained from the Central Person Register. Relative risks were estimated both by comparison with cancer incidence in the standardised general population and by internal analyses by use of Cox-regression.

Results Overall, significantly increased relative risks were seen for cancer of the pharynx (1.8; 1.0–3.0), lung (1.7; 1.4–2.2), testis (2.5; 1.2–4.9) and multiple myeloma (2.1; 1.0–4.4). Trends with increasing relative risk of lung cancer by increasing cumulative exposure to particles was observed (p<0.01) after adjustments for exposure to asbestos and tobacco smoking.

Conclusion This study supports that exposure to welding processed particles increases the risk for lung cancer. The increased of testicular cancer and multiple myeloma warrants further attention