An Epidemiological Study Of Lung Cancer In Asbestos Miners

Our plain-English summary of An Epidemiological Study Of Lung Cancer In Asbestos Miners, by D.C. Braun, T.D. Truan (1958).

The study

• Authors: D.C. Braun, T.D. Truan
• Published: Archives Of Industrial Health 17(6):634-653, June (1958)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 001618. The article is still under copyright, so we describe it here rather than post it.

In plain English

The authors followed Quebec asbestos miners with five or more years of exposure, employed in 1950, through 1955. Of 6,091 men, 133 were untraced; 187 of the remaining 5,958 died. Lung cancer was proved in 9 deaths and suspected in 3. The lung cancer death rate was 25.3 per 100,000 man-years of risk for proved cases, and 33.8 with suspected cases. Quebec rates predicted about eight deaths. With all 12, the excess approached but did not reach statistical significance. All 12 cases were in smokers, defined as men smoking over five cigarettes daily. None occurred among the 1,265 nonsmokers, a group that could include pipe or cigar smokers. The rate rose over the first 40 years of employment, which the authors related to aging, but overall did not appear to increase with length or degree of exposure. Counties around the mines had rates practically identical to eight comparison counties. The authors concluded that Quebec asbestos miners did not have a significantly higher lung cancer death rate than comparable segments of the general population. They noted Province rates were probably low.

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: Cohort study of asbestos miners followed from 1950 through 1955 using medical, death certificate and insurance records, with lung cancer death rates compared to general population rates for Quebec, its counties, Canada and the United States
• Who was studied: Asbestos miners in Quebec (Thetford Mines clinic records and workers at Asbestos, Que.) with five or more years of exposure who were employed in 1950. Office and other nonexposed personnel were excluded. The original cohort was 6,091; 133 were lost, leaving 5,958.
• Exposure: Asbestos dust in Quebec asbestos mining (fiber type not named in the article). Miners were placed in three exposure categories (I, II, III) based on a weighted average of years at different dustiness levels, with Category II assumed twice and Category III three times as dusty as Category I.
• Main results:
  • Of the 5,958 traced cohort members, 5,771 were still living in 1955 or later
  • Among the 187 known dead in the cohort, lung cancer was considered proved in 9 and strongly suggested (suspected) in 3
  • Rates were calculated per man-years of risk. Each man alive through a year counted as one man-year, and a man who died during the year counted as half a man-year.
  • Cohort lung cancer death rate based on the 9 proved deaths: 25.3 per 100,000 (per man-years of risk)
  • Including suspected cases, the cohort rate was 33.8 per 100,000, about 50% higher than the rate for the Province of Quebec
  • Based on general population rates for the Province, about 8 lung cancer deaths were expected in the cohort; 9 proved cases were observed
  • With all 12 proved plus suspected cases, the result was very close to, but not above, the 95% significance level, so the hypothesis of no higher mortality in the miners could not be rejected
  • In the age group 65 and over, the five deaths in the cohort (including one suspected case) gave a figure almost significant at the 95% level
  • No lung cancer occurred among the 1,265 nonsmokers; all proved and suspected cases were in smokers
  • Smokers were defined as men habitually smoking more than five cigarettes per day. Men who smoked only pipes or cigars were not counted as smokers.
  • The rate rose over the first 40 years of employment, which the authors considered plausible because the men were growing older
  • Overall, the cohort's lung cancer death rate did not appear to increase with length of exposure or with degree of exposure
  • Among 240 men with more than 40 years of employment, there were no proved lung cancer cases during the six years; one suspected case occurred in this group
  • The proved-case rate in the miners (25.3 per 100,000) was compared with 22.5 per 100,000 for the rest of the Province of Quebec
  • The lung cancer death rate in the eight counties immediately surrounding the asbestos-producing areas was practically identical to that of eight comparison counties elsewhere in the Province
  • Counting all records, there were 19 proved cases of primary lung cancer among the asbestos miners since 1940
  • Of the 19 proved lung cancer cases since 1940, information on asbestosis was available for 17, and asbestosis was present in 9
  • Among deaths through 1956 and into 1957 that the authors described as only suggestive of lung cancer, the diagnoses included mesothelioma
• The authors' conclusion: The authors concluded that asbestos miners in the Province of Quebec do not have a significantly higher death rate from lung cancer than comparable segments of the general population.
• Limitations the authors state:
  • The general population was probably not examined for lung cancer as diligently as the miners, so Province mortality rates may be low
  • The suspected but unproved cases strongly affect the results, and such cases would likely not be included in general population statistics
  • The general population rate for the age group 65 and over is likely understated
  • The combined age-group rates for Canada are approximations because exact populations in each age group were not known

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Statistical Significance.

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