IntroductionInorganic lead is considered a probable carcinogen by IARC (brain, lung, and stomach).MethodsWe conducted internal analyses via Cox regression of cancer incidence in two cohorts of lead-exposed workers with blood lead data (Finland, UK ), including almost 30 000 workers (20 752 in Finland and 9122 in the UK) and over 10 000 incident cancers. Our exposure metric was maximum annual blood lead (BL) test.ResultsThe combined cohort had a median maximum blood lead of 29 ug/dl, a mean first year BL test of 1977, and was 87% male. Forty-seven percent had more than 1 BL test. Significant (p<0.05) positive trends, using the log of each worker’s maximum BL, were found for brain cancer (malignant and benign combined), Hodgkins’s lymphoma, lung cancer, and rectal cancer, while significant negative trends were found for colon cancer and melanoma. A borderline significant positive trend (0.05≤p≤0.10) was found for esophageal cancer. Significant interactions by country were found only for lung cancer, with Finland showing a strong positive trend and the UK showing only a modest trend. However, in general trends were marked in Finland and weak or inconsistent in the UK.ConclusionsWe found strong positive incidence trends with increasing blood lead level, for several outcomes in internal analysis. Two of these, lung and brain cancer, were a priori suspected sites. Two of these outcomes are associated with smoking (lung and esophageal cancer), for which we had no data; however, we had no a priori reason to believe smoking differed between workers with different BL levels.