Methodological Approaches For Estimating The Number Of Cancers Caused By Occupational Exposure In Canada

Joanne KIM, Cancer Care Ontario, Canada
MCLEOD C. 2 , ARRANDALE V. 1,3 , PETERS C. 4,5,6 , DAVIES H. 2,4 , SONG C. 1 , LABRÈCHE F. 7 , LAVOUÉ J. 8 , NICOL A. 4,9 , PAHWA M. 1 , HUTCHINGS S. 10 , RUSHTON L. 10 , DEMERS P. 1,3,5

1 Occupational Cancer Research Centre, Cancer Care Ontario, Toronto, Canada
2 School of Population and Public Health, UBC, Vancouver, Canada
3 Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
4 Carex Canada, Burnaby, Canada
5 Carleton University, Ottawa, Canada
6 Institut Armand Frappier-INRS, Montréal, Canada
7 Institut de recherche Robert-Sauvé en santé et en sécurité du travail, Montréal, Canada
8 Université de Montréal, Montréal, Canada
9 Simon Fraser University, Burnaby, Canada
10 Imperial College London, London, United Kingdom

In recent years, several projects quantifying the burden of occupational cancer were conducted with increased methodological sophistication. We present the methods for incorporating more detailed exposure assessments and risk-relationships in the estimation of the attributable fraction (AF), developed for the Canadian Burden of Occupational Cancer project funded by the Canadian Cancer Society.
This project builds upon methods from a recent UK burden study to derive AFs using: relative risks (RR) from review of the literature, detailed assessment of the prevalence and level exposure developed by CAREX Canada, historical exposure trends, and a population model constructed from Canadian data. The methodological approach for each exposure-cancer site pair is adapted according to the level of detail in the available epidemiology and exposure data. The framework had three possible approaches:  Scenario A (overall exposed/unexposed), Scenario B (categorical exposure-response) and Scenario C (quantitative exposure-response).
An example of the most advanced approach (Scenario C) is crystalline silica.  Approximately 780,000 workers were exposed to silica 1961-2001, with 46% in the highest exposure group.  We incorporated annual exposure decreases of 4.1%, from an analysis of the Canadian Workplace Exposure Database. Based on the calculated cumulative exposure and the dose-response curve from Steenland et al. 2001, we estimated mean RRs of 1.36, 1.46, and 1.57 for the low, medium, and high exposure groups respectively. Estimated AFs for silica-related lung cancers were: 4.4% for males (549 cases), 0.2% for females (24 cases), and 2.4% overall (573 cases). Over half of the cases (56%) were from the construction industry.
We sought to increase the validity of the burden estimates by using Canadian exposure and population data. The methodological enhancements in incorporating detailed epidemiology and exposure assessment further increases the validity of estimates for specific industries and occupations, facilitating targeted risk reduction strategies to prevent occupational cancers.