Unsuspected exposure to asbestos and bronchogenic carcinoma

Our plain-English summary of Unsuspected exposure to asbestos and bronchogenic carcinoma, by K.M. Martischnig, D.J. Newell, W.C. Barnsley, et al (British Medical Journal, 1977).

The study

• Authors: K.M. Martischnig, D.J. Newell, W.C. Barnsley, W.K. Cowan, E.L. Feinmann, E. Oliver
• Journal: British Medical Journal
• Published: 1977;1(6063):746-9
• Type of article: Case report
• Cited by: 58 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002243).

Abstract

Two hundred and fifty men admitted to a thoracic surgical centre and matched controls were questioned in detail about their occupations after leaving school and their smoking habits. Of 201 men with confirmed bronchial carcinoma 58 gave a history of occupational exposure to asbestos, whereas only 29 out of 201 men matched for age and residential area who were admitted with other diseases gave such a history. This difference was statistically highly significant. The usual association of bronchial carcinoma with heavy smoking was observed, but asbestos exposure increased the risk of carcinoma whatever the level of smoking. These results are consistent with the hypothesis that asbestos exposure and the level of smoking act independently in causing bronchial carcinoma. The patients with carcinoma who had been exposed to asbestos presented on average three years earlier than those who had not been exposed. Asbestos regulations have eliminated the risk of exposure to workers in scheduled industries, so asbestos-induced diseases will probably be increasingly found among the many workers who have had incidental exposure to asbestos. It is therefore important to take a full occupational history.

In plain English

This was a case-control study. Over one year (April 1972 to March 1973), one of the authors questioned 250 men admitted to a thoracic surgical centre for investigation of possible lung cancer about every job held since leaving school and about their smoking. Of these, 201 were found to have lung cancer. None had asbestosis or had worked in asbestos manufacturing. Each man was matched by age with a male control from general hospitals in the same catchment area. Of the 201 men with cancer, 58 reported workplace asbestos exposure, compared with 29 of 201 controls. Averaged across smoking levels, the relative risk with exposure was 2.35 (95% confidence limits 1.39 to 3.97). The authors concluded that their figures pointed to independent roles for smoking and asbestos, though some synergism could not be ruled out. They also said the figures were consistent with risk being related to dose and duration of exposure, and with a possible safe lower limit. Exposed cancer patients presented at an average age of 59, against 62 for unexposed patients. The authors noted that unconscious interviewer bias could not be excluded.

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: Case-control study using detailed occupational and smoking interviews of hospital patients and age-matched hospital controls, with asbestos fibre counts in some resected lung specimens
• Who was studied: 250 men admitted to a thoracic surgical centre from April 1972 to March 1973 for investigation of possible lung cancer. 201 had confirmed lung cancer, and none had asbestosis or had worked in asbestos manufacturing. Controls were 201 men without bronchial carcinoma from general hospitals in the same catchment area, matched for age within two years. Fibre counts were done on 73 resected lungs (19 exposed, 54 unexposed).
• Exposure: Occupational asbestos exposure in jobs not ostensibly connected with asbestos, such as relagging pipes on ships, working near laggers, sweeping up asbestos debris, and using asbestos pads or sheets. Exposure was graded only by duration (1-5 years and 6 years and over). Fibre types were not named. Cigarette smoking was classified by the greatest number ever smoked regularly.
• Main results:
  • 58 of the 201 men with cancer reported asbestos exposure, compared with 29 of the 201 controls (chi-squared 12.3, P less than 0.001).
  • Exposure for over five years was reported by 37 patients with cancer and 12 controls (P less than 0.05).
  • Men smoking 25 or more cigarettes a day had a risk of carcinoma over nine times that of non-smokers.
  • The mean relative risk for asbestos exposure, averaged over all smoking groups, was 2.35 (95% confidence limits 1.39 to 3.97). For the 0-14, 15-24 and 25-or-more cigarettes a day groups, the relative risks were 1.08, 2.92 and 3.26. The authors said these were consistent with a constant risk from asbestos and also with some element of synergism.
  • Among the patients with carcinoma, exposed men presented at a mean age of 59 years and unexposed men at 62. The difference was significant.
  • The carcinoma was inoperable in 60% of exposed patients and 57% of unexposed patients, with no significant association.
  • Among 161 patients with tissue available, anaplastic carcinoma was found in 22 of 49 exposed men and 27 of 112 unexposed men, nearly twice as common among the exposed.
  • In lung fibre counts from 73 resected patients, there was no association between exposure history and very small fibre counts. A statistically significant association was found at levels from 10 000 fibres/g upwards.
• The authors' conclusion: The authors concluded that asbestos exposure increased cancer risk whatever the number of cigarettes smoked. They said their figures pointed to independent roles of smoking and asbestos, and were consistent with risk related to dose and duration of exposure and with a possible safe lower limit. They also concluded there is a risk for workers whose occupation may not be primarily associated with asbestos.
• Limitations the authors state:
  • The interviewer knew which men were being investigated for lung cancer, so unconscious interviewer bias cannot be excluded.
  • Patients at a thoracic surgical centre might have recalled asbestos exposure better because of concern about their illness.
  • Degree of exposure could be estimated only by duration.
  • The relevance of the fibre counts to the cancer is uncertain without lung samples from matched patients without cancer.
  • The numbers of adenocarcinomas were too small for firm conclusions.

Topics

Medical terms in this study, explained in our Lexicon: Bronchogenic Carcinoma, Habit, Carcinoma, Occupational Exposure, Asbestos Exposure, Occupational History.

Related studies

• An attempt to use the WHO typing in the histological classification of lung carcinomas — A. Reinilä, K. Dammert (1974)
• Cohort analysis of changes in incidence of bronchial carcinoma in a textile asbestos factory — J.F. Knox, R.S. Doll, et al. (1965)
• Morphology of bronchogenic carcinoma in workers formerly exposed to crocidolite at Wittenoom Gorge in Western Australia — J.E. Baker, D.C. Reutens, et al. (1986)
• Practical steps towards the prevention of bronchial carcinoma — R. Doll (1970)
• Smoking status, occupational asbestos exposure and bronchial location of lung cancer — C. Paris, J. Benichou, et al. (2003)
• Smoking, occupational risk factors, and bronchial tumor location: a possible impact for lung cancer computed tomography scan screening — M. Gonzalez, J.M. Vignaud, et al. (2012)

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