A proportionate mortality study on risk of bladder cancer among rubber workers

A proportionate mortality study was based on a sample of 6208 workers who were employed for at least 4 months during the period from 1917 to 1983 in a rubber tire manufacturing plant in Ontario, Canada. Identifying information of the workers was extracted from company records and linked to the Ontario Cancer Registry 1964-1983 death files. Among the cohort, 153 cancer deaths (146 male, 7 female), which included 6 bladder cancer deaths (all male), were found. For the six bladder cancer deaths, average age at time of first employment was 33.5 years, and average time from first employment to time of death was 31.8 years (with a range from 25.3 to 38.3 years). Proportionate mortality ratio (PMR) and mortality odds ratio (MOR), and their standardized forms (SPMR and SMOR), were calculated using the general population in Ontario for comparison. PMR and MOR were found to be 1.44 and 1.45, respectively. When the Ontario proportionate cancer mortality was applied to the cohort, adjusted for age and sex, 4.69 bladder cancer deaths were expected. The six bladder cancer deaths among the rubber workers therefore represented a 1.28-fold increase in standardized proportionate bladder cancer mortality when compared to the general population. Age and sex adjusted SMOR was found to be 1.29.