Asbestos exposures and thoracic neoplasms

Our plain-English summary of Asbestos exposures and thoracic neoplasms, by R.N. Jones (Seminars in Roentgenology, 1992).

The study

• Author: R.N. Jones
• Journal: Seminars in Roentgenology
• Published: 1992;27(2):94-101
• Type of article: Review
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004965).

Summary of the article

This narrative review, written for clinicians and radiologists, described the relationships between asbestos exposure and two thoracic cancers, lung cancer and diffuse malignant pleural mesothelioma, to help evaluate the risks from past exposures. For lung cancer, the author suggested a minimum latency of 10 years for the heaviest past exposures and 15 to 20 years for more typical later exposures. He noted that dose-response slopes varied with industrial process and fiber type. In the insulators' cohort, asbestos exposure was associated with about a 5-fold elevation of incidence, cigarette smoking with an 11-fold elevation, and both together with a 53-fold elevation. In other cohorts, exposure-related elevations usually lay between two-fold and three-fold. The author presented eight lines of evidence for the proposition that asbestosis, rather than asbestos itself, causes the exposure-related excess of lung cancer. He outlined three elements of a clinical-radiographic diagnosis of asbestosis: exposure, response and absence of confounders. For mesothelioma, he considered the data consistent with a minimum latency of 20 years. He noted that brief, domestic and neighborhood exposures to amphiboles increased risk, and that the risk from chrysotile was much lower. He concluded that a mesothelioma in a patient with past occupational asbestos exposure, even of only a few months and meeting the latency requirement, is probably the result of the exposure. He added that exclusive chrysotile exposure should not be assumed without overwhelming proof.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This 1992 article was a narrative review, not an original study. It covered published evidence on asbestos exposure and two chest cancers: lung cancer and diffuse malignant mesothelioma of the pleura. For lung cancer, the author judged that 10 years was a reasonable minimum latency for the heaviest past exposures, and 15 or 20 years for more typical later ones. Cited data from a cohort of insulators studied by Selikoff and colleagues showed roughly a 5-fold rise in lung cancer for asbestos exposure, 11-fold for smoking and 53-fold for both. In other cohorts, significant exposure-related rises in lung cancer incidence usually lay between two-fold and three-fold. The author argued that asbestosis (lung scarring), not asbestos itself, raises lung cancer risk, and asked readers to treat this idea with reserve and skepticism. For pleural mesothelioma, the review reported that occupational exposures to amphibole asbestos as brief as a few months raised risk. Crocidolite carried the highest risk and amosite the next-highest, while chrysotile's risk was much lower. There was no evidence that smoking raises mesothelioma risk.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Narrative review of published epidemiological, experimental and autopsy studies; no new data were collected
• Who was studied: No population was studied directly. The review drew on published studies of asbestos-exposed groups, including US and Canadian insulators, asbestos textile workers, friction materials manufacturers, Western Australian crocidolite miners, Nottingham gas mask factory workers, South African amphibole miners and Quebec chrysotile miners.
• Exposure: Occupational, domestic and neighborhood asbestos exposure, compared by fiber type (chrysotile, crocidolite, amosite, tremolite), together with cigarette smoking. Other naturally occurring fibers (zeolites in Turkey, tremolite in Greece) were discussed as other causes of mesothelioma.
• Main results:
  • For asbestos-related lung cancer, the author judged 10 years a reasonable minimum latency, based on studies of the riskiest past exposures. For more typical later exposures, the article says 15 or 20 years should be assumed.
  • In the insulators' cohort (Selikoff et al), lung cancer incidence was approximately 5-fold higher for asbestos exposure, 11-fold higher for cigarette smoking and 53-fold higher when both were present. There were no individual estimates of asbestos exposure intensity for this cohort.
  • In cohorts other than the insulators, significant exposure-related rises in lung cancer incidence usually lay between two-fold and three-fold.
  • The review found no demonstration of higher lung cancer risk from domestic exposures, such as in households of asbestos-exposed workers. Studies of neighborhood exposures had not shown higher lung cancer risk.
  • As one line of evidence that asbestosis drives lung cancer risk, the author cited a prospective mortality study (Hughes and Weill). In its exposed cohort, excess lung cancer deaths occurred only among workers with radiographic evidence of asbestosis at the start of follow-up.
  • On mesothelioma latency, the review cited two studies. In Western Australian crocidolite miners, 12 of 26 cases occurred between 15 and 19 years after first employment. In the updated insulators' data, only 5 of 458 mesothelioma deaths (1%) were thought to have occurred 15 to 19 years from onset of work exposure, which the author considered consistent with a minimum latency of 20 years.
  • Mesothelioma risk rose after occupational exposures to amphibole asbestos as brief as a few months. It also rose with domestic exposures to crocidolite or amosite and with neighborhood exposures to crocidolite. The review found no evidence that smoking increases mesothelioma risk.
  • By fiber type, crocidolite carried the highest mesothelioma risk and amosite the next-highest. The risk from chrysotile was much lower. The few mesotheliomas in chrysotile miners had been attributed to concurrent exposure to tremolite asbestos.
  • Among insulators, mesothelioma (pleural or peritoneal) accounted for about 4% or 8% of deaths, depending on whether the diagnosis came from death certificates or from review of diagnostic materials. The highest proportions of deaths from mesothelioma, 15% to 20%, followed crocidolite exposure in making filters for gas masks or cigarettes.
  • Apart from asbestos, the only other cause of mesothelioma with strong epidemiological support was regional exposure to other naturally occurring fibrous minerals: zeolites in certain areas of Turkey and tremolite in a remote area of Greece.
  • The author reported a consensus that pleural or peritoneal mesothelioma in a patient with past occupational asbestos exposure is probably the result of that exposure. This applies even when the exposure lasted only a few months, provided the latency requirement is met.
• The authors' conclusion: The author concluded that asbestosis is the mechanism through which asbestos exposure increases lung cancer risk, which makes an accurate diagnosis of asbestosis a marker of heightened risk.
• Limitations the authors state:
  • The author cautioned that the arguments for asbestosis as the cause of the lung cancer excess should be read with reserve and skepticism.
  • Many of the retrospective studies reviewed lacked smoking data on deceased individuals. Those studies had to assume or estimate past cigarette use in the exposed cohort.
  • The insulators' cohort, the most widely quoted source, had no individual estimates of asbestos exposure intensity.
  • The author noted that the minimum latency of mesothelioma is difficult to establish precisely. Mortality studies often used surrogates such as date of hire or union membership, and earlier exposures may have gone undetected.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Neoplasm, Lung Cancer, Pleural Mesothelioma, Latency, Dose-response relationship, Insulator, Mesothelioma.

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