This report focuses on ways that the use of scientific evidence in the adjudication of occupational cancer claims could be improved. It is important to state up front that this report will not include a discussion of compensation for cancer among firefighters. In Ontario (and many other jurisdictions), firefighters have received a broad set of presumptions that set them apart from all other workers. They are in a unique situation, with their own legislation and in this report, we have chosen to focus on the policies and processes that impact all other workers in the province covered by the WSIB.

It is also important to acknowledge that workers' compensation decisions are not based on science alone and that there are other legal and medical issues that are beyond the scope of this review. Some terms used in this report to describe scientific issues and principles may have a different meaning in a legal context. One particular example is the term work-related. Our interpretation of this term aligns with the Oxford English Dictionary's (OED) definition: having a connection or relation (sometimes causal) to the thing specified (i.e., work) (3). Similarly, our interpretation of the term work-relatedness aligns with the OED's definition: the state, condition, or fact of being related or connected to work (3). We recognize that this interpretation may not have the same meaning as the legal interpretation of work-related (i.e., arising out of and in the course of employment).

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:

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

The Ministry's desired outcomes were:

  • an expert independent assessment of how scientific evidence should be considered in evaluating whether a cancer is work-related
  • independent expert opinions on the additive implications of exposures, combined effects of exposures and synergies between different causes of disease
  • that Ontario workers and employers gain increased confidence that compensation laws and decisions take into account up-to-date science and best practices related to work-related cancers
  • that the MLTSD gain expert information to support evidence-based decision­ making when considering this technical area


To achieve the review's objectives, an environmental scan was undertaken to identify relevant legislation and related policy instruments (including regulations, policies, and adjudicative practice documents). 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. Information was collected from online sources and was supplemented by a series of in-person meetings with representatives from the 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 U.S., New Zealand, Australia, and Europe. In addition, the WSIB provided analyses of both submitted and accepted cancer claims. Lastly, searches of the published scientific literature were conducted to identify key studies that would be helpful for preparing the part of the report dealing with scientific principles.