In 1910, a Royal Commission was undertaken in Ontario to look into workers' compensation schemes. Led by Sir William Meredith, this review took three years to complete and culminated in the publication of the Meredith Report in 1913 and the passage of modern workers' compensation legislation in the province in 1914. In his recommendations, Meredith articulated that the system should be based on the following principles: no fault, non-adversarial, security of benefits, employer pays, and collective liability, and should be administered by an independent public agency with exclusive jurisdiction (1). These principles became the foundation for the "Historic Compromise", in which injured workers gave up the right to sue their employer in exchange for guaranteed benefits, provided by a non-adversarial system for as long as the disability lasted. The compromise aimed to provide fair compensation for workers who became injured or ill because of their work, while protecting employers from legal action and potential bankruptcy. While this compromise was beneficial to all, it has always worked best for injuries and illnesses where the effects are immediate and evidence of exposure to hazards and attribution are clear.

Cancer and other long-latency diseases are challenging for workers' compensation systems. As our knowledge of the chronic health effects of workplace exposures has increased, compensation for workplace cancer has become an important issue for workers employed in hazardous industries, as well as the unions that represent them and their employers. However, it has emerged as a public issue in recent decades through reports in the mass media and greater awareness of the link between exposure to workplace carcinogens and cancer. The handling of cancer claims has been a frequent source of frustration for all parties involved, but most importantly for workers diagnosed with cancer and their families. As a province with a large manufacturing sector and other industries, such as mining, where hazardous exposures were common in the past, challenges regarding the impact of past exposures and their consequences are likely to continue. It is in this context that the Ontario Ministry of Labour, Training and Skills Development commissioned this report.


This report was prepared with the assistance of several colleagues as well as the staff of the Occupational Cancer Research Centre (OCRC). Anya Keefe, former Director of the WorkSafeBC Research Secretariat, conducted the environmental scan of relevant practices in other jurisdictions, assisted with the content in the report related to policy and its intersection with science and provided editorial assistance throughout. Dr. Sarah McCormick-Rhodes aided with the literature review to support the explanation of relevant scientific principles in the report. Stephanie Ziembicki, Kate Jardine, and Elizabeth Rydz also provided assistance with literature reviews, graphics, and editing. Thanks to the staff and leadership of the WSIB and the MLTSD staff, who were extremely helpful in explaining the adjudication process, providing any statistics requested, providing historical context, and helpful suggestions. Special thanks to Katherine Lippel, Professor at the University of Ottawa and the Canada Research Chair on Occupational Health and Safety Law, for educating me on the legal vs. scientific perspectives on compensation and to Lesley Rushton, Emeritus Reader in Occupational Epidemiology at Imperial College London and chair of the UK Industrial Injuries Advisory Council, for her extremely valuable advice regarding international comparisons. I would also like to thank my colleagues from across Canada and around the world for providing their views on compensation and directing us to useful resources. Lastly, I would like to thank the workers, injured worker advocates, employers, and union representatives who shared their views and experiences with the workers’ compensation system in Ontario.

List of abbreviations used in this report

Advisory Board on Radiation and Worker Health
Advisory Board for Toxic Substances and Health
Administrative practice documents
Association of Workers' Compensation Boards of Canada
Biological Exposure Index
Commission des norms, de l'équité, de la santé et de la sécurité du travail
Canadian Workplace Exposure Database
Department of Energy
Energy Employees Occupational Illness Compensation
Energy Employees Occupational Illness Compensation Program Act
General Electric
International Agency for Research on Cancer
Industrial Injuries Advisory Council
International Labour Organization
Integrated Management Information System
l'Institut national de recherche et de sécurité pour la prevention des accidents du travail et des maladies professionnelles (French National Research and Safety Institute for the Prevention of Occupational Accidents and Diseases)
Institut de recherche Robert-Sauvé en santé et en sécurité du travail
Institute for Safety, Compensation and Recovery Research
Labor and Industries
Medical Surveillance
Ministry of Labour, Training and Skills Development
Ministère de la santé et des services sociaux
National Dose Registry
National Institute for Occupational Safety and Health
Occupational Cancer Research Centre
Occupational Health Clinics for Ontario Workers
Operational Policy Manual
Occupational Safety and Health Administration
Office of Workers' Compensation Programs
Permissible exposure limit
Partnership for Work, Health and Safety
Special Exposure Cohort
Site Exposure Matrices
Safety & Health Assessment & Research for Prevention
Salt Lake Technical Center
Scientific and Technical Advisory Committee
Threshold Limit Value
University of British Columbia
Workplace Safety and Insurance Board
World Trade Center
World Trade Center Health Program

Executive summary

Mandate of the review

In January 2019, the Ontario Ministry of Labour, Training and Skills Development (MLTSD) requested an independent review to provide advice to the Ministry on the following questions:

  • How can scientific evidence best be used in determining work-relatedness in an occupational cancer claim, particularly in cases with multiple exposures?
  • Are there any best practices in other jurisdictions that Ontario should consider adopting?
  • What scientific principles should inform the development of occupational disease policy?


An environmental scan was undertaken to identify relevant legislation and policy instruments. The scan was followed by a more detailed examination of legislative frameworks and key policy instruments to identify the principles governing the compensation of occupational cancer and how entitlement is determined in Ontario. Information was collected from online sources and was supplemented by a series of in-person meetings with representatives from the Workplace Safety and Insurance Board (WSIB) and the MLTSD, as well as in-person meetings or phone calls with stakeholders in Ontario and occupational health researchers from across Canada, the US, New Zealand, Australia, and Europe. In addition, the WSIB provided data on both submitted and accepted cancer claims. Lastly, searches of the published scientific literature were conducted to identify key studies dealing with relevant scientific principles.

Occupational cancer in Ontario

Part 2 of the report sets out the context of occupational cancer and compensation in Ontario. Based on our current knowledge of the causes of cancer, it is estimated that approximately half of all cancer is preventable. While there is still much that we do not know about the causes of cancer, many workplace carcinogens have been identified. The OCRC's Burden of Occupational Cancer Project estimated that there are approximately 3,000 cancers diagnosed per year in Ontario due to occupational exposure to 16 of the most well-established carcinogens.

Adjudication and management of occupational cancer claims in Ontario are handled by the WSIB's Occupational Disease and Survivor Benefits Program. In determining entitlement to compensation for occupational cancers specifically, and occupational diseases more generally, the key adjudicative question to be resolved is that of causation (i.e., what caused the cancer).

Three general principles govern how causation is evaluated and entitlement is determined:

  • Employment does not have to be the predominant or primary cause.
  • Absolute certainty is not required.
  • The worker is afforded the benefit of the doubt.

Entitlement is determined by reference to presumptions provided in Schedules 3 or 4 of O. Reg 175/98, by application of operational policies in Chapters 16 and 23 of the Operational Policy Manual (OPM), and on a case-by-case basis. According to the WSIB, the key step in all occupational disease claims – and the one that is most relevant to this review – is information gathering. In this step, the decision-maker gathers, analyzes and weighs employment history, detailed exposure history, medical history, current scientific evidence on occupational exposures and diseases, and relevant personal information. As appropriate, the decision-makers will consult with medical specialists to resolve questions on causation and work-relatedness.

Compensated claims for deaths from occupational cancer in Ontario have increased dramatically since 1997, surpassing those for traumatic injuries in 2005 and more than doubling them by 2010. Fatal claims, however, only represent part of the cancer picture. Data provided by the WSIB on all cancer claims show that 4,044 cancer claims were filed between 2009 and 2018 and that 1,678 (or 41.5%) were accepted (not including claims related to the firefighter presumptions). On average, the WSIB has accepted 170 cancer claims per year (130 of which are for asbestos-related cancers). This is only a small fraction of the 3,000 estimated occupational cancers predicted for Ontario (including approximately 800 due to asbestos).

Fatal cancer claim rates are the easiest to compare across Canadian jurisdictions and Ontario's is the highest of the major provinces. The rate of all accepted cancer claims in Ontario in 2018 was 2.9 per 100,000 insured workers, which is significantly lower than many countries in the European Union. In a 2016 report, for example, the rate of accepted occupational cancers claims per 100,000 insured workers ranged from 4.7 in Belgium to 15.1 in Germany. The rates in Italy, Denmark and France fell in between (at 6.3, 6.9 and 11.4, respectively).

Scientific principles relevant to this review

Determining causation in the context of workers’ compensation is a complex process primarily governed by legal principles, but, hopefully, informed by scientific principles as well. There are a number of national and international agencies and organizations that assess whether chemicals, forms of radiation, or other factors cause cancer, based on scientific principles and the use of peer-reviewed and publicly available scientific evidence. The most widely recognized of these internationally, and in Canada, is the International Agency for Research on Cancer (IARC) which has identified hundreds of known, probable, and possible associations between workplace exposures and cancer. While our knowledge of what causes cancer has greatly increased and continues to do so, the sophistication with which we approach attribution in workers’ compensation has not always kept pace.

Part 3 of the report focuses on the following theories and principles that are relevant to determining the work-relatedness of cancer:

  • multi-stage theories of carcinogenesis emphasize the importance of considering multiple exposures as well as the time intervals between multiple exposures in the carcinogenesis process
  • all cancers are likely to have multiple causes. If these causes are independent of each other, we generally assume that the risk of both is the sum of the two. However, in some cases there may be synergy between causes and the joint effects can be much greater
  • induction and latency periods are sometimes treated as a property of a disease. However, they are actually a property of the relationship between each exposure and the disease, and each exposure could have different effective time periods
  • biological processes, such as the development of disease, generally have what is termed a normal distribution (a bell-shaped curve) while, for practical purposes, we generally use a discrete range of years or other units when assessing the length or timing of exposure or its latency. Discrete time ranges for exposure and latency based on nice round numbers are useful, but it should be recognized that these ranges will not apply to all individuals

Why the compensation of occupational cancers is so challenging

In adjudicating a claim, decision-makers seek to determine whether the disease is due to the nature of the worker's employment (i.e., is the disease work-related?). Part 4 briefly presents some major challenges faced by the workers' compensation system in Ontario and elsewhere. These include:

  • a lack of recognition by primary care providers is the major factor underlying the gap between the estimated true number of occupational cancers and the number of cancers compensated in Ontario
  • epidemiology (which is the science concerned with the occurrence of disease in populations) assesses exposure and risk at the group level, not at the individual level. Epidemiology is useful in developing presumptive criteria, informing policy guidelines or establishing general causation, but caution needs to be used when applying its results to establish causation in individual cases
  • exposure to multiple established or suspected human carcinogens is common. However, too few epidemiologic studies have looked at the impact of multiple occupational exposures because their focus is almost always on establishing whether a single agent is, or is not, a cause of disease
  • the documentation or estimation of historical exposure to workplace carcinogens is a critical component to making science-based judgements on the work-relatedness of occupational cancer. However, documenting exposure retrospectively is challenging, particularly in the absence of quantitative measurements and other data
  • the term "cluster" has been used in recent years to describe an unusual number of cancers occurring among a relatively small group of people that may be due to new and emerging hazards and a perceived excess risk in a larger population who were exposed to recognized hazards. Unfortunately, there is no agency in Ontario with the responsibility to investigate occupational clusters and neither the WSIB nor the MLTSD have the necessary research capacity

Relevant practices in other jurisdictions

Part 5 of the report highlights relevant practices in other jurisdictions. Many workers’ compensation systems have presumptive lists of occupational diseases, some of which are modelled on the List of Occupational Diseases published by the International Labour Organization (ILO). However, there is a wide variation in the number of cancers recognized and the exposures/working conditions associated with them. For example, in the UK, cancers associated with 40 exposures/working conditions are currently included on the Prescribed Diseases List. In jurisdictions around the world scientific advisory panels have been created to provide independent advice for the ongoing updating of national presumptive lists, as well as to inform the development and optimization of policies and processes about causation/work-relatedness.

A number of examples of internal and partnered scientific capacity exist that bring together policymakers, researchers and data resources with the goal of improving compensation and preventing occupational diseases. The report highlights two Canadian and two international examples: the Partnership for Work, Health and Safety (British Columbia) and the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (Québec), the Safety & Health Assessment & Research for Prevention (Washington State, U.S.), and the Institute for Safety, Compensation and Recovery Research (Australia). This part of the report also highlights several large-scale exposure databases (e.g., the Canadian Workplace Exposure Database developed by CAREX Canada), exposure assessment approaches used by the U.S. National Institute for Occupational Health and Safety, as well as a historical exposure matrix created under contract for Unifor to assist with the compensation claims of their members.

Observations and recommendations

Part 6 of the report sets out a series of observations and recommendations to support the WSIB's efforts to improve evidence-based decision-making.

Recommendations to update presumptive lists and cancer-relevant policies

  1. the WSIB should update and greatly expand the list of presumptions regarding cancer in Schedules 3 and 4 to reflect the current state of scientific knowledge. Presumptions should be based on exposure to carcinogenic agents or processes, and not specific employers, in order to be more broadly applicable. In updating and expanding its presumptive lists, the WSIB may want to consider using criteria such as that used in the independent scientific review undertaken of Australia's deemed diseases list (2). Similar to that review, I would recommend that the following three criteria be used:
    • evidence of a strong causal link between the disease and occupational exposure, defined on the basis of inclusion in IARC Group 1 (i.e., definite human carcinogen), a systematic review of the evidence, or multiple good quality studies showing a causal relationship between the disease and the occupational exposure
    • clear diagnostic criteria for any disease included in a scheduled list to ensure questions don't arise as to whether or not the claimant really has the disease that is the subject of the claim
    • the occupational disease comprises a considerable proportion of the cases of that disease overall in the exposed population
  2. the WSIB should update and expand all of the policies relevant to adjudication of cancer claims to reflect the current state of scientific knowledge. We have identified several areas for which new policies are needed
    • a policy that explains how exposure to multiple carcinogens is handled. Given the current state of knowledge regarding the impact of multiple exposures, the effects of exposure to carcinogens impacting the same cancer site should be considered additive, unless there is evidence to the contrary
    • a policy that states clearly how non-occupational exposures, particularly cigarette smoking, are weighted relative to occupational exposures. As with multiple occupational exposures, the relationship should be considered additive unless there is evidence for a synergistic effect
  3. the WSIB should create an independent, standing Scientific Review Panel to review and recommend changes to the schedules and policies, to review and approve scientific reports, and to assist in the selection of external consultants and researchers. The Panel should be composed of independent scientists with a broad range of expertise, including epidemiology, toxicology, occupational medicine, and occupational hygiene. The process for choosing members should allow for stakeholder input, including the opportunity for worker representatives and employers to nominate scientists. Scientists with expertise in occupational cancer and occupational disease are a scarce resource in Canada and the scientific challenges are similar across the country. Ontario could consider sharing the support of such a panel with other jurisdictions. This would not only increase efficiencies and leverage other resources, but also increase the independence of the panel

Recommendations to enhance scientific capacity

  1. the WSIB needs to increase its internal scientific capacity to at least its previous levels. This should include scientists with graduate level training in epidemiology, toxicology and exposure science (such as occupational hygiene)
  2. stronger partnerships with external research centres, including those already funded with WSIB funds, are needed for research on emerging issues and gaps of importance to Ontario. Such partnerships should encourage the development of surveillance systems to support evidence-based decision making in adjudication and to assist in identifying emerging issues, including previously unrecognized excesses of cancer
  3. provincial capacity needs to be developed to investigate cancer clusters and other emerging issues. Ideally that should be in the MLTSD, where it is independent of the WSIB, and could also focus on prevention of future disease as well as compensation. This would require increased research capacity within the Ministry. MLTSD could seek partnerships with other branches of government. For example, Public Health Ontario currently investigates suspected clusters of environmental origin and has appropriate expertise to provide assistance. Historically, MLTSD's physicians undertook these investigations. MLTSD needs to rebuild its scientific capacity

Recommendations to improve access to exposure data for compensation (and prevention)

  1. adjudication should be improved by better access to electronic exposure data. While MESU is useful, it could use a better interface and does not cover all circumstances or time periods needed. The WSIB should attempt to partner with the Canadian Workplace Exposure Database (CWED) which contains the MESU data, but also contains exposure data collected by other provinces to cover a wider range of exposure
  2. MLTSD should lower data access barriers and create better mechanisms to provide exposure-related data to WSIB. In addition, exchange of data in both directions between MLTSD and WSIB could also contribute to prevention. The Ministry should consider this in the context of its statutory obligations and the existing privacy regulatory framework in Ontario. Facilitating this may require the Ministry to computerize records and, potentially, statutory changes
  3. MLTSD should collect copies of exposure monitoring results from employers at the time of inspections and computerize those results to facilitate access to exposure monitoring data. As above, the Ministry should consider this recommendation in the context of Ontario's existing privacy regulatory framework and statutory changes may be needed
  4. WSIB should explore opportunities to work with external research organizations to digitize historical exposure or employment records for high-risk industries, such as was done with the Mining Master File. Such efforts could also be taken using internal resources

Recommendations to improve recognition through medical education

  1. physician education is a challenging area that deserves more investigation. While a detailed review of this issue is beyond the scope of this report, it is important that medical education be improved in Ontario to increase the recognition of occupational cancer