subject: Pulmonary Tumors in Asbestos Treated Rats Require New Studies [print this page] In order to examine the association between fibrosis and tumor production in more detail, groups of animals with and without pulmonary tumors can be assembled. One interesting study is called, "The relationship between fibrosis and cancer in experimental animals exposed to asbestos and other fibers." By J M Davis and H A Cowie - Institute of Occupational Medicine, Edinburgh, Scotland. Environ Health Perspect. 1990 August; 88: 305309. Here is an excerpt: "Abstract - The association between occupational asbestos exposure and the development of both pulmonary fibrosis or asbestosis and pulmonary carcinomas is well documented. It has been suggested that the two pathological conditions are associated with asbestos-related carcinomas developing from areas of asbestosis and not occurring when exposure has been too low to produce this type of pulmonary scarring. Experimental inhalation studies so far published have not been designed to examine this association specifically, but many publications have reported that asbestos samples producing high levels of fibrosis is experimental animals are also very carcinogenic. Samples of asbestos or man-made fibers that produce little fibrosis also produce few tumors. These works are reviewed. In order to examine the association between fibrosis and tumor production in more detail, groups of animals with and without pulmonary tumors and with individual fibrosis measurements were assembled from a number of inhalation studies undertaken over a period of years at this Institute. It was found that animals with pulmonary tumors had almost double the amount of pulmonary fibrosis as animals of similar age that did not. In a few of the animals where tumors were found at an early stage of development, their origin from fibrotic areas could be confirmed, although in most cases where tumor deposits were widespread this was not possible. Experimental confirmation of the site of origin of most pulmonary tumors in asbestos-treated rats would require new studies with rats examined specifically at an age when early tumors would be expected."
Another interesting study is called, "Absence of synergism between exposure to asbestos and cigarette smoking in asbestosis." By Samet JM, Epler GR, Gaensler EA, Rosner B. -
Am Rev Respir Dis. 1979 Jul;120(1):75-82. Here is an excerpt: "Abstract - To assess both independent and synergistic effects of exposure to asbestos and cigarette smoking on the development of asbestosis, survey data from 4 groups of workers exposed to asbestos were analyzed with multivariate statistical models. Survey methods were standardized and included for the 383 subjects a respiratory symptoms questionnaire, occupational history, physical examination, pulmonary function testing, and a chest radiograph. Exposure to asbestos and cigarette smoking were assessed by questionnaire. Synergism between the 2 exposures was not present for previously identified manifestations of asbestosis including bilateral fine crackles, clubbing, dyspnea, radiographic abnormality, decreased forced vital capacity, and decreased single-breath diffusing capacity of the lung for CO. However, additive, independent effects of these 2 exposures were present for each of these parameters."
Another interesting study is called, "Routes of asbestos exposure and the development of mesothelioma in an English region." By D Howel, L Arblaster, L Swinburne, M Schweiger, E Renvoize, P Hatton - Occup Environ Med 1997. Here is an excerpt: "Abstract - OBJECTIVES: To investigate the contribution of exposure to asbestos through different routes in the development of mesothelioma. METHODS: Case-control study. 185 confirmed cases of mesothelioma and 160 controls were identified, when death had occurred between 1979 and 1991 in four health districts in Yorkshire. The surviving relatives were interviewed to ascertain lifetime exposure to asbestos. Adjusted odds ratios (ORs) of exposure to asbestos (through occupational, paraoccupational, and residential routes) were calculated for cases and were compared with controls. RESULTS: Likely or possible occupational exposure to asbestos was more common in cases than in controls (OR 5.6, 95% confidence interval (95% CI) 3.1 to 10.1). After excluding those with likely or possible occupational exposure, likely or possible paraoccupational exposure was more common in cases than controls (OR 5.8, 95% CI 1.8 to 19.2). Only six cases of mesothelioma were identified as being solely exposed to asbestos through their residence, compared with nine controls. The OR for residential exposure to asbestos varied between 1.5 and 6.6, depending on which potential industrial sources were included, but the 95% CIs were so wide that slightly reduced or greatly increased odds comparing cases with controls could not be excluded. CONCLUSION: Study results support previous evidence that occupational and paraoccupational exposure to asbestos is associated with developing mesothelioma. Despite a rigorous search, purely residential exposure seemed to account for only 3% of identified cases. No firm conclusion can be drawn about the risks from residential exposure alone, as many of the study subjects could also have been occupationally or paraoccupationally exposed to asbestos."
We all owe a debt of gratitude to these fine researchers for their important work. If you found any of these excerpts helpful, please read the studies in their entirety.
Pulmonary Tumors in Asbestos Treated Rats Require New Studies
