A case-referent study of lung cancer, occupational exposures and smoking. II. Role of asbestos exposure

Our plain-English summary of A case-referent study of lung cancer, occupational exposures and smoking. II. Role of asbestos exposure, by H. Kjuus, R. Skjaerven, S. Langård, et al (Scandinavian Journal of Work, Environment & Health, 1986).

The study

• Authors: H. Kjuus, R. Skjaerven, S. Langård, J.T. Lien, T. Aamodt
• Journal: Scandinavian Journal of Work, Environment & Health
• Published: 1986;12(3):203-9
• Cited by: 51 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. 000409).

Abstract

In a hospital-based case-referent study of 176 incident lung cancer cases, ascertained during a five-year period from two county hospitals, the role of asbestos exposure and smoking has been studied. Information on asbestos exposure was obtained from personal interviews, and allocated to four exposure categories, according to the intensity and duration of the exposure. Twenty-five percent of the cases and 10% of the referents had been moderately to heavily exposed to asbestos during their working career. A statistically significant trend in risk ratio related to the degree of exposure was observed, with a more than fourfold risk among the heavily exposed. The strongest association was found between asbestos exposure and small cell carcinoma, and the weakest association between asbestos exposure and adenocarcinoma. Very high risk ratios were observed among asbestos-exposed subjects who were heavy smokers, and the interaction observed between asbestos and smoking conformed more closely to a multiplicative model than to an additive one. The results suggest that the observed association between lung cancer and occupational exposures in this study was, to a large extent, due to asbestos exposure. Information on such exposure was missing in 90% of the medical records of these patients.

In plain English

This hospital-based case-referent study in southeast Norway compared 176 male cases and 176 referents recruited 1979–1983. Most cases had lung cancer; four had mesothelioma, a separate pleural tumor the authors included. Exposure, from interviews and questionnaires, was graded 0 to 3 by combining intensity and duration. The article did not name fiber types. Some exposure was found in 60% of cases and 42% of referents. Moderate-to-heavy exposure (grades 2–3) was found in 25% and 10%. Risk rose significantly with grade, exceeding fourfold in the highest grade. Light or indirect exposure was not significantly elevated (RR 1.2). The association was strongest for small cell carcinoma (RR 3.0) and weakest for adenocarcinoma (RR 2.2), though the authors noted low numbers. Very high risk ratios were seen with heavy smoking plus heavy asbestos exposure. A tentative analysis found the combined effect fit a multiplicative better than an additive model. Only four of 40 cases' medical records checked contained asbestos information. The authors concluded the results suggest asbestos largely explained the study's link between lung cancer and occupational exposures. They noted that cases exaggerating exposure could not be ruled out.

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: Hospital-based case-referent (case-control) study
• Who was studied: 176 male cases and 176 referents, recruited 1979–1983 from the medical wards of Telemark County Hospital and Vestfold County Hospital in southeast Norway. The cases were classed as lung cancer (ICD 162, 163). Four of them were mesotheliomas, which the authors described as a separate tumor of the pleura but included in the study.
• Exposure: Lifetime occupational asbestos exposure (fiber types not specified), from personal interviews and a questionnaire. Intensity and duration were combined into four grades: 0 (none), 1 (uncertain, indirect, light/sporadic), 2 (moderate for 1 to under 10 years, or heavy for under one year) and 3 (moderate for 10 years or more, or heavy for one year or more). Main settings of grade 2–3 exposure included electrochemical process and maintenance work, shipbuilding and ship engine maintenance. Nonoccupational environmental exposure was not taken into account.
• Main results:
  • Some asbestos exposure (grades 1–3) was found in 60% of cases (N = 105) and 42% of referents (N = 76).
  • Moderate-to-heavy exposure for more than one year (grades 2–3) was found in 44 lung cancer patients (25%) and 17 referents (10%).
  • The lung cancer risk ratio showed a statistically significant trend with degree of asbestos exposure (likelihood ratio G = 12.2, 3 df, p = 0.007), with a more than fourfold risk in the highest exposure group.
  • For indirect or light/sporadic exposure (grade 1), the risk ratio was not significantly elevated (RR = 1.2). This estimate was adjusted for smoking (five levels) and urban/rural status.
  • The association was mainly found in the age group 60–69 years, where moderately exposed subjects had a threefold increased risk.
  • Comparing grades 2–3 with grades 0–1 by tumor type, the strongest association was for small cell carcinoma (RR = 3.0) and the weakest for adenocarcinoma (RR = 2.2). The authors noted that these histology findings were based on low numbers.
  • There were four mesotheliomas among the cases, three of them classified as asbestos-exposed grade 2 and 3. The authors described mesothelioma as a separate tumor of the pleura. They included these cases because the total burden of asbestos-related tumors of the respiratory system was of interest.
  • Among those with moderate or heavy exposure, the odds ratio for lung cancer was highest for maintenance workers in the electrochemical industry (RR = 8.6). It was also high for shipyard and ship engine maintenance workers (RR = 7.2).
  • Asbestos-exposed (grades 2–3) moderate smokers (10–19 cigarettes/day) had a relative excess risk of 16.9, against 4.5 expected if the effects were additive. Exposed heavy smokers had 28.8, against 14.9 expected. The index of interaction was 3.8 and 1.9 for the two smoking levels.
  • Under a multiplicative model, the expected risk ratio for asbestos plus moderate smoking was 9.8, against an observed 17.9. For asbestos plus heavy smoking it was 34.8, against an observed 29.8.
  • When asbestos and smoking were subdivided into four and five levels, very high risk ratios were observed for the combination of heavy smoking and heavy asbestos exposure.
  • Several associations between lung cancer and occupational-title-based measures became nonsignificant when adjusted for asbestos exposure.
  • In the medical records of 40 lung cancer cases from Vestfold County Hospital, only four records gave information on asbestos exposure. No referent records had such information. The interviews found grade 2–3 exposure in 30% of these cases and 10% of the referents.
• The authors' conclusion: The authors concluded that their results suggest the observed association between lung cancer and occupational exposures in this study was, to a large extent, due to asbestos exposure. They described the stratified smoking analysis as a tentative quantification. That analysis suggested the interaction more likely conforms to a multiplicative model than to an additive one.
• Limitations the authors state:
  • The authors could not rule out that cases exaggerated their asbestos exposure (recall bias), possibly influenced by public awareness of asbestos compensation claims.
  • The study area included electrochemical plants with past asbestos use, so the authors noted that the study's external validity might be low.
  • Sparse numbers in subgroups forced use of a two-level asbestos variable. In the smoking analysis, the reference category (0–9 cigarettes/day) was not truly unexposed.
  • The authors state that the quantitative relationship between asbestos and smoking depended strongly on how the variables were categorized, especially the unexposed category.
  • The histology findings were based on low numbers.

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: Lung Cancer, Occupational Exposure, Asbestos Exposure, Carcinoma, Adenocarcinoma.

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