Document oy3awDG6Qx1ZpK8R9Ooy3rdD

if the tumor, i. 'I ...re is only one Delation with pleu' association may ntal. The presentmrs are invariably it ions include part ruction. tally one of rapid >rs, the average suruptoms is approxineal tumors, 13 to :ver, and in one se tter 3 years (187). gn the course, the ' classification .iielioma (205). snlment litely made only by e a number of reae a positive diagnoe, even when adevailable. These incell types within a : of the mixed type, limary tumors else- 1 that diagnojrate in most . In addition, there ing agreement belogic characteristics ifiiculty reflected by .*r of cases, less than (206), subsequently review panels. This ant in clinical medint distinction is benam tumor, than in ek to investigate the f asbestos exposure, nostic criteria in ex. is all important. Jmor and within-luaentioned previousdevelopment of the biopsy needle, other ve been used to intosis. Thus, the presrr the pleural fluid in tumor tissue by J08) may be of some tween mesothelioma nit is not the definielieved to be (207). le _ fluids, by light ASBESTOS-RELATED LUNG DISEASES 213 anti electron microscopy, may offer useful con terial from more than 1,000 cases of pneumocon tributory evidence. A series of papers under the iosis published in 1951 (211). From these, it general title "Assessment of Methods Used in appeared that asbestosis was associated with a the Studies of the Biological Effect of Asbestos much higher lung cancer risk than other pneu to Paihology" (7, pp. 53-31) provides a most moconiosis, with 15 to 20 per cent of men re convenient and up-to-date summary of these corded as having asbestosis dying front this methods, their precision, and general applic cause. This risk was reported to have further in- ability. creased considerably in Britain by 1963 (10), The radiologic appearances vary according to and a similar increase in lung cancer risk during the stage to which the disease has progressed. the same decades has been reported front Ger Common features are the presence of a pleural many (Jacob, 5, p. 536). The emergence of lung effusion, lobufated tumor masses that may be cancer as an important threat to the health of visible onlv after removal of the pleural fluid, asbestos workers is attributed to the improvement chest wall masses, satellite lung lesions, and, oc in dust conditions, with less mortality from asbes casionally, hydropneumothorax (209). tosis occurring after longer periods of exposure In a review oi treatments (13, p. 277) Elmes and, therefore, survival of workers through the pointed out that there is no effective curative long latent period of lung cancer (63). treatment, although surgical excision, local Subsequent epidemiologic studies have amply and/or systemic cytotoxic therapy, and radio confirmed the association between asbestos ex therapy have all been tried. He also pointed out posure and lung cancer, mortality experience several features that suggest a considerable con being the chief method of study (63, 67, 82); tribution of the body's defense mechanism, both however, table 7 indicates that despite the con in the formation of abnormal tissue and in the sistently increased relative risk in these reports, shaping of its clinical course. Relative to the there are considerable between-sludy differences first point is the apparently low dose of exposure as to its degree. Some of these differences, must capable of eliciting a response; relative to the certainly be ascribed to between-study differences second is the not infrequent occurrence of chest in the methods used to calculate risk (217). injuries and/or infections at the onset oi the particularly in such factors as composition of the clinical course, and the sometimes rapid dissem risk group (in terms of age, years of exposure, ination, apparently provoked by treatments, and length of follow-up), and the nature of the such as radiation or cytotoxic drugs. For these control or reference group, which could be cith reasons, he believes that this tumor may eventu er a low-exposiue group within the working ally turn out to be controllable through improv population, or an appropriate reference popu ing body defenses. Thus, it is not surprising that lation derived from national statistics. In addi the use of BCG vaccine in treatment is a matter tion, most studies deal with relatively small of great current interest, with, as yet, no defini numbers of deaths (less than 100 in all but 2 tive evidence on which to base clinical action. of the studies), so that calculation would inevi Meanwhile, therapy is symptomatic, and diag tably be influenced by the addition or loss of nostic measures should be kept to a minimum. one case. Finally, differences in exposure dose Removal of fluid for diagnostic examination and smoking habits are other relevant factors and to relieve breathlessness should be done as for which standardization is seldom possible. As infrequently as possible. Indeed, as Elmes notes, Wagner and associates point out, however, "an the establishment of a precise diagnosis in life, additional lesson to be learnt from the appar given the absence of a potentially curative treat ent conflict of evidence is the need to pay more ment, is an academic, rather than a clinically attention to the type of asbestos and to the useful, exercise. physical state of the respirable faction of the dust" (218). and the evidence that there are real differences in risk associated with the diff Carcinoma of tha Lung Associated with erent fiber types, as well as the different types Asbestos Exposure of exposure to the same fiber, is becoming more An association between asbestosis and bron convincing. Such differences, however, have a chial carcinoma, suspected in the 1930s on the greater significance in the field of environmen basis of individual case reports (210), was sub tal control and safety standards than in the prac sequently confirmed in two British reports, one tice of clinical medicine. by the Chief Inspector of Factories, issued in The interaction of cigarettes and asbestos ex 1947, and the second, an analysis of autopsy ma posure as risk factors, clarified to some extent by