The International Agency for Research on Cancer recently classified inorganic lead as a probable carcinogen,
while organic lead remained unclassifiable. Uncertainty persists because of limited epidemiologic evidence. The
authors addressed the relation between occupational exposure to lead and the risk of 11 types of cancer among
men in a case-control study conducted in Montreal, Quebec, Canada, in the 1980s. Incident cases (n ¼ 3,730) and
general population controls (n ¼ 533) were interviewed to elicit information on job history and potential confounders.
Expert chemists translated each job into a list of substances to which the subject had potentially been exposed.
Exposure to lead was classified into three categories: organic lead (3% of subjects ever exposed), inorganic lead
(17%), and lead in gasoline emissions (39%). Odds ratios and 95% confidence intervals were estimated by logistic
regression using two control groups: general population controls and cancer controls. Stomach cancer was
associated with organic lead when the authors used population controls (odds ratio (OR) ¼ 3.0, 95% confidence
interval (CI): 1.2, 7.3) and cancer controls (OR ¼ 2.0, 95% CI: 1.1, 3.8) and with substantial exposure to lead in
gasoline emissions when they used cancer controls (OR ¼ 2.9, 95% CI: 1.4, 5.9). There was no association with
inorganic lead and little evidence for associations with other cancer types.