There are three investigations in which an association between pleural plaques and lung cancer was sought at autopsy (Table 7). The percentage of deaths in which autopsy was done was provided in only one report; it was only 25 percent. Age was the only factor controlled for, and no study controlled for smoking habits. The estimated relative risk was slightly elevated in all three studies, but none was statistically significant. Thus, these investigations provide no support for the hypothesis. The weight of evidence in this review is against the hypothesis that persons with asbestos-related pleural plaques are at increased risk of lung cancer compared with unexposed persons or the general population. Ten of the 13 studies examined were negative. Furthermore, the three positive studies were all most seriously deficient in terms of design and potential for bias and confounding.
Cohort studies entail a design that permits assessment of pleural plaques as a precursor to lung cancer risk; therefore, this type of investigation is most suitable for this purpose. Case-control studies herein, and autopsy studies always, provide information only on the prevalence of both pleural plaques and lung cancer at one point in time, when cancer is already present; therefore, they examine only for an association without giving any information on the temporal relationship between the two entities. In addition, low autopsy rates allow for significant bias, which may account for the small elevations, statistically insignificant, of the odds ratios in the three reports described herein.
Table 7—Autopsy Studies of Pleural Plaques and Lung Cancer
|Characteristics and Results||Meurman, 1966®||Mollo, 1984»||Wain et al, 198430|
|Location of study||Finland||Turin, Italy||Durham NC|
|Percent of deaths autopsied||Not given||25||Not given|
|Factors controlled||Mean age similar, both sexes included||age, men only||Mean age similar, men only|
|Control for smoking||No||No||No|
|Statistical method||X2, Yates’ correction||Age-adjusted relative, risk, 95% CL||X2|
|No. with plaques||103||199||25|
|No. with lung cancer (%)||3 (2.91)||14 (7.0)||4 (16)|
|No. without plaques||152||566||409|
|No. with lung cancer (%)||4 (2.63)||26 (4.6)||55 (13.6)|
|Degree of association||Odds ratio = 1.11||Relative risk = 1.51||Odds ratio = 1.23|
|P value or 95% CL||>0.70||0.75-3.09||>0.70|
|Comment||Odds ratio calculated from data||Relative risk calculated by authors||Odds ratio calculated from data|