Review: Asbestos-related pleural plaques are not associated with the risk for lung cancer
ACP J Club. 1993 Nov-Dec;119:91. doi:10.7326/ACPJC-1993-119-3-091
Weiss W. Asbestos-related pleural plaques and lung cancer. Chest. 1993 Jun;103:1854-9.
To determine whether an association exists between asbestos-related pleural plaques and the risk for lung cancer in the absence of diffuse parenchymal fibrosis (asbestosis).
Studies on asbestos-related disease and the etiology and epidemiology of lung cancer were identified using Index Medicus and MEDLINE (1965 to June 1992) and using bibliographies of relevant papers.
Epidemiologic studies with a cohort or case-control design and autopsy prevalence studies were selected if they were in English or had an English language abstract and addressed the relation between pleural plaques unaccompanied by asbestosis and lung cancer. Only the most recent report of each study was used.
Location of research, type of exposure to asbestos, type of asbestos, description of cohorts, method of assessing pleural plaques, follow-up duration and completeness, possible biases, control for confounders, consideration of latency, statistical methods used, and study size. Relative risks (RRs) or odds ratios (ORs) for cancer, 95% confidence intervals (CI) or P values, and numbers of observed and expected cases of cancer in cohort studies were extracted or calculated.
6 cohort studies (3040 participants), 4 case-control studies (51 persons with plaques among 360 patients with cancer and 61 persons with plaques among 415 control participants in 3 case-control studies), and 3 autopsy studies (327 persons with pleural plaques and 1127 without) were included. 2 cohort studies completed in the same city showed RRs for lung cancer of 2.37 ( P< 0.005) and 1.88 (P < 0.02), whereas the RRs for the other 4 studies did not show any differences (RRs 0.81 to 1.33). The case-control study with the weakest methods (no information was given on the statistical method used or the numbers of cases and controls, and only 1 rater read the chest radiographs unblinded) had an OR of approximately 4 (P < 0.01). The other ORs were 0.75, 0.97, and 1.12 (P > 0.05 for each). The 3 autopsy studies showed no association between asbestos-related pleural plaques and lung cancer (OR 1. 1, P > 0.7; OR 1.23, P> 0.7; and RR 1.51, Cl 0.75 to 3.09). Of the 13 studies, only 2 cohort studies adjusted for smoking status.
10 of 13 studies show no association between pleural plaques from asbestos and lung cancer. The 3 studies that show an association (2 cohort studies and 1 case-control study) have methodologic flaws.
Source of funding: None.
For article reprint: Dr. W. Weiss, 3912 Netherfield Road, Philadelphia, PA 19129, USA. Telephone 215-849-4971.
Asbestos has been associated with pleural plaques, parenchymal fibrosis (asbestosis), lung cancer, and mesothelioma. Of these, pleural plaques are generally regarded as markers for asbestos exposure but are assumed to be of little clinical significance.
The risk for lung cancer in asbestos workers is increased as much as 4 or 5 times. In cigarette smokers, the risk is increased approximately 10 times, whereas for those with both exposures the risk approximates a 50-fold increase among insulation workers in the United States and Canada.
One possibility is that the risk is not increased with pleural plaques alone but is increased only in those with parenchymal fibrosis. In this review, Weiss analyzed asbestos workers with pleural plaques to determine if they are at increased risk for lung cancer, and he concluded that insufficient evidence exists to state that pleural plaques are an independent risk factor. The methodologic weaknesses of previous studies are highlighted in Weiss' review. For example, lack of controlling for cigarette smoking is a potentially fatal flaw in the previous studies, especially because the risk for lung cancer is greater with smoking than with asbestos exposure. The reliance on chest roentgenograms for determination of parenchymal fibrosis in previous studies may also have obscured the different risks for parenchymal fibrosis and for isolated pleural plaques, and it is unfortunate that high-resolution computed tomography was not used in more of the studies (1). The currently available data do not support an association between pleural plaques and lung cancer in asbestos-exposed workers, and this supports the hypothesis that the excess lung cancer cases associated with asbestos exposure occur in those who develop parenchymal fibrosis.
Kurt Hegmann, MD
Medical College of WisconsinMilwaukee, Wisconsin, USA