A cohort study of 43,826 male pensioners of the Canadian National Railway Company was conducted. The cause of death of 17,838 pensioners who died between 1965 and 1977 was ascertained by computerized record linkage to the Canadian national mortality data base. The main finding was an elevated risk of lung cancer for those employed in occupations involving exposure to diesel fumes and coal dust, with highly significant dose-response relationships observed. That such association may be due in part to smoking cannot be excluded; but in view of the widespread exposure to diesel fumes, the finding warrants further investigation. The present study also demonstrated the utility and feasibility of large-scale occupational cohort studies conducted with the use of computerized record linkage to national mortality records.
An historical prospective mortality study of INCO's Ontario work-force has been conducted. A cohort of approximately 54 000 men, employed in all aspects of the extraction and refining of copper and nickel from the Sudbury ore deposit, have been followed for mortality between 1950 and 1976. A total of 5 283 deaths were identified by computerized record-linkage to the Canadian Mortality Data Base of death certificates. The analysis focuses on mortality from cancer of the nasal sinuses, larynx, lung, and kidney. Little evidence was found for increased mortality from laryngeal or kidney cancer, but lung and nasal cancer deaths were clearly elevated in men exposed to the two Sudbury area sinter plants and at Port Colborne in the leaching, calcining, and sintering department. The standardized mortality ratio (SMR) for lung cancer increases linearly with increasing duration of exposure and there is no evidence of a threshold. The nasal cancer mortality rate also rises linearly with duration of exposure. While lung cancer has a greater excess in the Sudbury sinter plant than at Port Colborne, the reverse is true for mortality from nasal cancer, which is ten times more frequent at Port Colborne than at Sudbury.
The possibility that excess cancers result from occupational exposures in oil refineries has generated a great deal of interest. Ecological studies and case-control studies in the general population have suggested a positive association between oil industry activity and cancer rates, with more direct evidence provided by studies of refinery employees. The eight investigations of cancer risks among refinery employees are critically reviewed. The methodological strengths and weaknesses of these studies are evaluated with an emphasis on the likely impact on the results. While the results are markedly inconsistent across studies, there is some suggestion of excess risks for melanoma and for brain, stomach, kidney, and pancreatic cancers. Problems with exposure characterization, latency, and potential confounding factors limit all of the studies that were reviewed.
Intratracheal instillations of 7H-dibenzo(c, g)carbazole (DBC), a tobacco smoke component, into Syrian golden hamsters, resulted in preneoplastic lesions and benign and malignant respiratory neoplasms. Neoplastic progression was associated with specific changes in the extracellular matrix (ECM), dependent on the stage of tumor development. DBC-induced tracheobronchial squamous metaplasia was associated with an increase in collagen type I and type III deposition in the subepithelial ECM, as observed by computer-assisted image analysis of immunohistochemical staining for the aminoterminal propeptides of collagen type I (PINP) and collagen type III (PIIINP). Increased collagen matrix synthesis was detected in dysplasia by in situ hybridization of alpha1(I) mRNA for collagen I and alpha1(III) mRNA for collagen type III after continued exposure to DBC. In well-differentiated squamous cell carcinomas with an expansive growth pattern, collagen deposition increased, as did fiber size. In moderately differentiated neoplasms, basement membrane (BM) destruction and invasion was associated with a destructive growth pattern and decreases in collagen synthesis and the deposition of new collagen. Preserved deposition of mature collagen was detected by staining for the telopeptide of collagen type I propeptide. In less differentiated tumors, ECM development was minimal, with few and small fibers, possibly explaining the rapid development of these neoplasms. Transforming growth factor beta (TGFbeta1) immunoreactivity was increased in hyperplastic epithelium and well differentiated neoplasms and decreased in dysplasia and less differentiated squamous cell carcinomas, while TGFbeta2 and TGFbeta3 expression was also distinct in neoplastic cells. Collagen synthesis and epithelial differentiation were associated with an increased number of myofibroblasts in the ECM and with increased TGFbeta3 immunoreactivity in differentiated cells and in the matrix. The nature of the composition of the ECM was related to neoplastic growth and progression when analyzed by computer-associated image analysis, revealing alterations in collagen structure, size, and shape.
The effect of different summary measures of worklife exposure on the estimation of risk is reported. Two matched case-referent studies associating sulfuric acid exposure and cancer from Baton Rouge and southern Ontario were used. Five summary exposure measures were converted to discrete levels of exposure through the selection of equivalent percentile points on each measure's respective percentage frequency distribution for logistic regression modeling purposes. The southern Ontario data set exhibited only minor differences across all five exposure measures. The Baton Rouge data set, however, produced different results, and the time-dependent measures appeared to underestimate risk. It is possible, therefore, to obtain different estimates of risk depending on the exposure measure selected. It is recommended that, in the absence of proved models for assessing exposure, a variety of summary measures be used to estimate risk. This approach would facilitate the comparison of findings across studies.
On the basis of hygienic studies in foundries of nickel plants conditions for and character of the formation of industrial aerosols, their physico-chemical properties are studied. The data obtained indicate significant pollution in the occupational areas with ++nickel-containing aerosols. High carcinogenic risk has been shown to characterize the foundries. A dependence of workers' mortality due to malignant tumours on nickel and its compounds content in the air of occupational area has been shown. A complex of health-improving measures aimed at reducing oncological morbidity of workers in foundries of nickel plants is presented. A priority significance is attributed to application of new technological processes in production.