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Working in the rubber industry is associated with increased cancer risks, particularly for cancers of the lung, larynx, urinary bladder and leukaemia.1 Most epidemiological studies, however, still reflect working conditions back to the 1940s. As occupational exposures were lowered considerably since the late 1970s, prospective health surveillance is warranted to assess the effectiveness of exposure control.
The cohort included all blue‐collar workers of 13 participating rubber manufacturing companies in western Germany who were hired after 1 January 1981 and worked for at least 1 year until the end of follow‐up. Follow‐up started on 1 January 1982 and ended on 31 December 2000, but was censored at the age of 85 years.
The vital status was ascertained via population registries. Death certificates were requested from community health departments and underlying causes of death were coded by professional nosologists according to the ninth revision of the International Classification of Diseases (ICD‐9).
The mortality experience of the cohort was compared with the mortality of the corresponding population of western Germany. Standardised mortality ratios (SMRs) and exact 95% confidence intervals were calculated stratified by gender and nationality and standardised by calendar year and 5‐year age groups using the PAMCOMP software.2 A lag period of 10 years was applied to SMR analysis of all‐cause and all‐cancer mortality—that is, the first 10 years after starting work were ignored.
The cohort included 8210 male and 1387 female German and 2476 male and 229 female non‐German blue‐collar workers. Vital status ascertainment was almost complete (98% for German; 94% non‐German). Death certificates were obtained for 90% of the German and 67% of the non‐German decedents; only four cancer deaths were observed among non‐German decedents.
Among German cohort members 25% have been employed for more than 10 years in the rubber industry and 47% have been hired between 1981 and 1989. The majority of deaths have occurred in the last five years of follow‐up.
Among German men the decreased mortality (table 11)) was mainly due to lower mortality from diseases of the circulatory system and cancer. For women the all‐cause mortality and all‐cancer mortality was higher than expected.
Among male German rubber workers mortality from cancers of the oral cavity and pharynx was increased based on a total of three cases, and lung cancer mortality was lower than expected. Among female German rubber workers increased SMRs on the basis of only one or two deaths were observed for several cancer sites, including stomach, lung and leukaemia. No death from bladder cancer was observed in the entire cohort with 0.3 expected deaths for German men.
We observed a healthy worker effect among German male rubber workers and increased all‐cause and all‐cancer mortality among female rubber workers. With lagging, the healthy worker effect for cancer‐related deaths was diminished. Based on small numbers statistically non‐significant increases in mortality from cancers of the oral cavity, pharynx, lung, stomach and leukaemia among men or women were noted. The results were not consistent across gender.
The cohort is reasonably large. Nevertheless, the inception cohort design, imposed by the goal to study working conditions in the modern rubber industry, the maximum follow‐up of 20 years and the hiring of predominantly young workers into the rubber industry limited the statistical precision.
The SMRs are not adjusted for potential confounders such as tobacco smoking and alcohol consumption. Among men, decreased mortality from lung cancer and chronic liver disease argue against strong confounding. Among women mortality from lung cancer and chronic liver disease was increased and confounding cannot be ruled out. Conversely, both diseases may also be caused by occupational exposures in the rubber industry3,4 and smoking is only a moderate risk factor for stomach cancer and leukaemia.
The observed overall pattern of increased cancer‐specific SMRs is consistent with our previously reported findings among rubber workers employed in earlier periods3,4,5 and with findings from epidemiological studies among rubber workers in other countries.1 Only one other study has investigated carcinogenic risks in the modern rubber industry.6 Interestingly, the only statistically significant increase in mortality was noted for cancer of the testis, which was also increased in our cohort. Yet, the results for incidence of testicular cancer in the British cohort did not support the mortality findings. Due to registration deficits in Germany, the investigation of cancer incidence in our cohort is not feasible.
The cohort is reasonably large but still too young to provide conclusive evidence. Increased cancer risks are consistent with previous results among German rubber workers employed in earlier periods. Pooled analyses of ongoing cohort studies in the modern rubber industry are needed to allow for a robust interpretation.
The study was funded and supported by the Berufsgenossenschaft der Chemischen Industrie, Heidelberg and the Wirtschaftsverband der deutschen Kautschukindustrie e V, Frankfurt/M. The authors wish to acknowledge the important contributions of the late Dr Helmut Cordes, occupational physician at one of the participating companies, whose competent and determined support was essential for the initiation and conduct of this cohort study.