Author's response to 'Re: Exposure to asbestos and the risk of colorectal cancer mortality: a systematic review and meta-analysis by Kwak et al'

Our plain-English summary of Author's response to 'Re: Exposure to asbestos and the risk of colorectal cancer mortality: a systematic review and meta-analysis by Kwak et al', by K. Kwak, D. Paek, K.E. Zoh (Occupational and Environmental Medicine, 2020).

The study

• Authors: K. Kwak, D. Paek, K.E. Zoh
• Journal: Occupational and Environmental Medicine
• Published: 2020;77(9):656-657
• Type of article: Letter, Comment
• Read it: PubMed · Publisher

In plain English

This is a letter in which the authors replied to a comment by Dr Boffetta on their earlier systematic review and meta-analysis of asbestos exposure and colorectal cancer deaths. Dr Boffetta had raised possible overlap between cohorts. The authors re-examined their material and agreed that some cohorts could have been counted twice. They kept an Italian pool of asbestos worker cohorts out of the analysis because it included environmental exposures and so did not meet their original inclusion rules. They removed seven possibly overlapping studies, which had made up 15% of the weight, and recalculated the pooled standardised mortality ratios (SMRs), keeping the most recent five cohorts. The authors reported that the subgroup results were basically the same, with only minor changes in significance. The 'miscellaneous' industry subgroup changed from a non-significant increase to a significant decrease, 0.86 (0.74–0.998). The 'various' industry subgroup became significant, 1.35 (1.24–1.47). The subgroup for adequacy of follow-up lost significance. The authors concluded that the main finding, an increased risk of colorectal cancer death in workers exposed to asbestos, stayed statistically significant after these exclusions.

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: Authors' reply letter reporting a reanalysis of their own systematic review and meta-analysis
• Who was studied: Cohort studies of asbestos-exposed workers from the authors' earlier meta-analysis. Seven potentially overlapping studies were removed, and the most recent five cohorts were kept.
• Exposure: Occupational exposure to asbestos. The letter does not name specific fiber types for the analysis.
• Main results:
  • The authors agreed with Dr Boffetta that some cohorts might have been counted twice in the original analysis.
  • The Italian pool of asbestos worker cohorts was still judged ineligible because it was a pooled study that included environmental exposures.
  • The seven excluded cohorts had carried 15% of the weight in the meta-analysis.
  • Subgroup results were basically the same after reanalysis, with only minor changes in significance for some subgroups.
  • In the 'miscellaneous' type of industry subgroup (7 studies), the pooled SMR became 0.86 (0.74–0.998). The authors describe this as a change from a non-significant increase to a significant decrease.
  • In the 'various' type of industry subgroup (6 studies), the pooled SMR was 1.35 (1.24–1.47), which the authors say gained significance.
  • In the subgroup of studies with virtually complete follow-up (23 studies), the pooled SMR was 1.15 (0.95–1.38). The authors say this subgroup lost significance.
  • In the reanalysis, the pooled SMR was 1.49 (1.26–1.75) for insulation industry studies (4 studies).
  • In studies where the lung cancer SMR was high (2 or more; 17 studies), the pooled colorectal cancer SMR was 1.44 (1.29–1.60).
  • In studies where the lung cancer SMR was low (less than 2; 22 studies), the pooled colorectal cancer SMR was 0.99 (0.85–1.16).
  • The increased risk of colorectal cancer death in asbestos-exposed workers remained statistically significant after the seven studies were excluded.
• The authors' conclusion: The authors concluded that the main finding, an increased risk of colorectal cancer death in workers exposed to asbestos, was almost the same in the reanalysis as in the original analysis.
• Limitations the authors state:
  • The authors acknowledged that the original meta-analysis may have double counted overlapping cohorts.

Topics

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

Medical terms in this study, explained in our Lexicon: Colorectal Cancer, Systematic Review, Meta-Analysis.

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