Occupational exposure to asbestos and risk of cholangiocarcinoma: a population-based case-control study in four Nordic countries

Our plain-English summary of Occupational exposure to asbestos and risk of cholangiocarcinoma: a population-based case-control study in four Nordic countries, by A. Farioli, K. Straif, G. Brandi, et al (Occupational and Environmental Medicine, 2018).

The study

• Authors: A. Farioli, K. Straif, G. Brandi, S. Curti, K. Kjaerheim, J.I. Martinsen, P. Sparen, L. Tryggvadottir, E. Weiderpass, G. Biasco, F.S. Violante, S. Mattioli, E. Pukkala
• Journal: Occupational and Environmental Medicine
• Published: 2018;75(3):191-198
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To assess the association between occupational exposure to asbestos and the risk of cholangiocarcinoma (CC).

Methods: We conducted a case-control study nested in the Nordic Occupational Cancer (NOCCA) cohort. We studied 1458 intrahepatic CC (ICC) and 3972 extrahepatic CC (ECC) cases occurring among subjects born in 1920 or later in Finland, Iceland, Norway and Sweden. Each case was individually matched by birth year, gender and country to five population controls. The cumulative exposure to asbestos (measured in fibres (f)/ml × years) was assessed by applying the NOCCA job-exposure matrix to data on occupations collected during national population censuses (conducted in 1960, 1970, 1980/81 and 1990). Odds ratios (OR) and 95% CI were estimated using conditional logistic regression models adjusted by printing industry work.

Results: We observed an increasing risk of ICC with cumulative exposure to asbestos: never exposed, OR 1.0 (reference category); 0.1-4.9 f/mL × years, OR 1.1 (95% CI 0.9 to 1.3); 5.0-9.9 f/mL × years, OR 1.3 (95% CI 0.9 to 2.1); 10.0-14.9 f/mL × years, OR 1.6 (95% CI 1.0 to 2.5); ≥15.0 f/mL × years, OR 1.7 (95% CI 1.1 to 2.6). We did not observe an association between cumulative asbestos exposure and ECC.

Conclusions: Our study provides evidence that exposure to asbestos might be a risk factor for ICC. Our findings also suggest that the association between ECC and asbestos is null or weaker than that observed for ICC. Further studies based on large industrial cohorts of asbestos workers and possibly accounting for personal characteristics and clinical history are needed.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

In plain English

This study asked whether work-related asbestos exposure was linked to cholangiocarcinoma (bile duct cancer) inside the liver (intrahepatic) or outside it (extrahepatic). It was a case-control study in Finland, Iceland, Norway and Sweden, using census and cancer-registry records. It included 1458 intrahepatic and 3972 extrahepatic cases among people born in 1920 or later. Each case was first matched to five population controls; after exclusions, 6773 and 18,221 controls remained in the analyses. Asbestos exposure was estimated from census job titles using a job-exposure matrix, not measured for individuals. For intrahepatic cancer, risk rose with estimated cumulative exposure. People in the highest category (15.0 or more fibres/mL × years) had an odds ratio of 1.7 (95% CI 1.1 to 2.6) compared with never-exposed people. No association was seen for extrahepatic cancer. The authors noted they lacked information on liver disease and personal habits, and that job-based estimates could misclassify exposure. The authors concluded that the study supports the hypothesis that occupational asbestos exposure is a risk factor for intrahepatic but not extrahepatic cholangiocarcinoma. They said further studies are needed to establish causality.

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: Population-based case-control study nested in the Nordic Occupational Cancer (NOCCA) cohort, with each case originally matched to five population controls
• Who was studied: Cases were people born in 1920 or later in Finland, Iceland, Norway and Sweden, diagnosed between the first available census and the end of follow-up (2003 to 2005, depending on country). Each case was matched by gender, birth year and country to five population controls. People without informative occupational codes were then excluded. The final analyses included 1458 intrahepatic cases with 6773 controls, 3972 extrahepatic cases with 18,221 controls, and 2801 cases whose site could not be determined.
• Exposure: Occupational exposure to any form of asbestos fibres or asbestos-containing material. Exposure was estimated by applying the NOCCA job-exposure matrix to job titles recorded in the 1960, 1970, 1980/81 and 1990 censuses. It was expressed as ever/never exposure, maximum intensity, duration, and cumulative exposure in fibres/mL × years. No specific fibre types were distinguished.
• Main results:
  • For intrahepatic cholangiocarcinoma, the odds ratio for cumulative exposure of 15.0 f/mL × years or more, compared with never exposed, was 1.7 (95% CI 1.1 to 2.6).
  • For intrahepatic cholangiocarcinoma, risk increased across cumulative exposure categories. The odds ratios were 1.1 (0.1 to 4.9 f/mL × years), 1.3 (5.0 to 9.9), 1.6 (10.0 to 14.9) and 1.7 (15.0 or more), with p for trend 0.001 in Table 2.
  • No association was found between asbestos exposure and extrahepatic cholangiocarcinoma.
  • For intrahepatic cholangiocarcinoma, ever-exposed people had an odds ratio of 1.2 (95% CI 1.0 to 1.4) compared with never exposed. The highest maximum-intensity category (0.80 f/mL or more) had an odds ratio of 1.6 (95% CI 1.2 to 2.2).
  • For intrahepatic cholangiocarcinoma, every category of exposure duration showed an odds ratio of 1.2 compared with never exposed.
  • With a 20-year lag (ignoring exposure in the 20 years before diagnosis), the highest cumulative exposure category for intrahepatic cholangiocarcinoma had an odds ratio of 2.1 (95% CI 1.2 to 3.7), based on 19 cases and 47 controls. The lagged and unlagged models did not differ substantially in fit.
  • The overall intrahepatic estimates were driven by men, because very few women had exposure levels above 1.1 f/mL × years.
• The authors' conclusion: The authors concluded that this is the first large population-based study supporting the hypothesis that occupational asbestos exposure is a risk factor for intrahepatic, but not extrahepatic, cholangiocarcinoma. They said further studies are needed to establish causality and to define the size of the risk.
• Limitations the authors state:
  • There was no information on non-work confounders such as liver diseases and personal habits.
  • Exposure could be misclassified because it was assessed from job titles, without individual asbestos measurements.
  • Full work histories and employment dates were not available. The authors assumed everyone worked from age 20 to 65 and that exposure was similar between censuses.
  • There was no information on non-occupational sources of asbestos exposure.
  • Asbestos exposure levels in the study population were relatively low compared with the highest levels worldwide.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Case-Control Study, Cumulative Exposure, Odds Ratio, Asbestos Exposure.

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