Is breast cancer an occupational disease?

There may be a long road ahead yet to more widespread recognition of breast cancer as an occupational disease

Is breast cancer an occupational disease?
Certain workplaces may present carcinogenic hazards that can lead to the development of cancers – including breast cancer.

Every year in October, Canada — and the rest of the world — observes Breast Cancer Awareness Month. According to the Canadian Cancer Society, breast cancer is still the most common cancer in Canada and the second leading cause of cancer death among Canadian women. Not traditionally thought of as an occupational disease (i.e., a health condition or disorder caused by work environment or tasks), this may be because scientific research into the topic is still relatively limited.

According to Canada’s Public Health Agency, one in eight women in Canada is expected to develop breast cancer during their lifetime and one in 33 will die of it. In 2019, there were an estimated 26,900 Canadian women diagnosed with breast cancer and 5,000 deaths. Eighty-three per cent of breast cancers occur in women over 50 years of age, but breast cancer among younger women is increasing.

The Public Health Agency of Canada states that there is no single cause of breast cancer, listing risk factors that are largely genetic or lifestyle related. At the time of writing, environmental exposures are not listed as factors.

In a recent article for The Conversation, Jane E. McArthur of the University of Windsor writes that primary prevention efforts for tackling breast cancer need to improve. This means better policy, regulation and legislation — specifically around environmental exposures to breast carcinogens.

McArthur cites research in her article stating that environmental factors may contribute in 70 per cent to 90 per cent of breast cancer cases, with only five to 10 per cent of cases related to genetics.

What is an occupational cancer?
According to the Canadian Centre for Occupational Health and Safety (CCOHS), an occupational cancer is cancer that is wholly or in part caused by exposure to a carcinogen at work. The CCOHS says that the most common types of occupational cancer are lung and bladder cancer and mesothelioma (cancer that begins in the tissue that lines vital organs such as the lungs, heart and stomach). Lung cancer and mesothelioma are notably associated with asbestos exposure.

Cancers are broadly associated with certain types of carcinogens. In the case of breast cancer, the CCOHS says that high-risk substances such as ethylene oxide*, ionizing radiation** and polychlorinated biphenyls (PCBs)*** could be carcinogenic. In addition, for breast cancer, shiftwork that involves circadian disruption (biological timing or day/night cycle) is an example of a high-risk occupation that can potentially increase the risk of breast cancer.

*Ethylene oxide is used in a wide range of products including detergents, solvents, plastics, etc. For example, it is used in health-care facilities to sterilize critical items in some cases (according to the U.S. Centres for Disease Control).

**According to the World Health Organization, “Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized.”

***PCBs are used in industrial and commercial applications, including electrical, heat transfer and hydraulic equipment.

Which industries are at risk?
In Our Chemical Selves: Gender, Toxics and Environmental Health, edited by Dayna Nadine Scott (published by UBC Press in 2015), researchers discuss the incidence of breast cancer among plastics industry workers (“Chapter 10: Plastics Industry Workers and Breast Cancer Risk: Are We Heeding the Warnings?” by Margaret M. Keith, James T. Brophy, Robert DeMatteo, Michael Gilbertson, Andrew E. Watterson and Matthias Beck). Their research examined workers’ exposure to carcinogens and endocrine-disrupting chemicals in the plastics injection moulding industry. Plastics manufacturing employs around 91,000 people in Canada, with 48 per cent of plastics firms in Ontario alone.

In 2003, the researchers began collecting data for a case-control study. Over six years of data collection, the researchers interviewed 1,006 women with breast cancer. They found that a total of 184 participants surveyed worked in the plastics industry at some point in their lives. The study also found that the risk for breast cancer “more than doubled among women who had worked in automotive plastics manufacturing for ten years and who had been assessed as having been highly exposed to EDCs and/or carcinogens.” The researchers also note additional studies that could demonstrate a link between plastics workers and incidences of breast cancer.

“Despite the strong evidence that women in the plastics industry environment are exposed to agents that can cause cancer, to our knowledge no plastics worker in Canada has ever received workers’ compensation following a diagnosis, nor have any breast cancers been recognized as work-related” said the authors (as we will see below, this is no longer the case).

“Furthermore,” the authors say, “no public inquiries or commissions have convened to examine the risks to women posed by exposures in the plastics industry, nor have there been any focused institutionalized research initiatives, prevention campaigns, educational programs, or regulatory changes.”

Additional studies have shown that, aside from plastics, specific sectors showed significant excesses in breast cancer risk. These include farming, food canning, metalworking and the bar/casino/race track sector.

Does gender play a role?
The authors of the study cited above note that gender and class may play a part in why there is limited research around breast cancer among these workers. In addition, fear of job loss or delocalization play a part as to why workers may not speak up. Furthermore, with breast cancer, lifestyle risks and genetic susceptibility play a part.

One of the paper’s authors, James T. Brophy of the University of Windsor, posits that “occupational disease adjudication as well as all occupational health regulatory practices, exhibit deep-seated gender bias.”

In an article published in the American Journal of Industrial Medicine in 2003, Shelia Hoar Zahm and Aaron Blair conclude that our current understanding of occupational exposures and breast cancer is most likely based on gender and is outdated:

“Estimates that 1% of cancer among women is attributable to occupation are based on research conducted mainly in the 1970s among men in developed countries. These studies do not reflect the dramatic changes in the participation of women in the workplace or the patterns of employment of women in developing countries.

“The proportion of women in the paid workforce, the amounts and types of unpaid labor, the distribution of women by economy sector, the scale of the workplaces, the allowable exposure levels in the workplace, and implementation of controls have changed over time and vary internationally,” say Zahm and Blair (“Occupational Cancer Among Women: Where Have We Been and Where Are We Going?”).

British Columbia (Workers’ Compensation Appeal Tribunal) v Fraser Health Authority
In June 2016, the Supreme Court of Canada ruled in favour of three B.C. health-care workers, Katrina Hammer, Patricia Schmidt and Anne MacFarlane. The three women argued that they had developed breast cancer as a result of their jobs (the women, among seven who also developed breast cancer, worked in a lab at Mission Memorial Hospital).

Years before the final Supreme Court decision, the Workers’ Compensation Board denied their initial application, arguing that their cancers were not occupational diseases.

Nevertheless, the Workers’ Compensation Administrative Tribunal ruled in 2010 and 2011 that the cancers were, in fact, linked to the workplace. However, the British Columbia Court of Appeal then ruled that the WCAT decisions were wrong because, among other reasons, there was no causal evidence between the cancers and the women’s workplace environment.

The Supreme Court decision raised many questions in the legal community, notably around burden of proof, scientific evidence and what kind of precedent the case sets on both a provincial and federal level. Importantly, this case doesn’t necessarily mean that breast cancers are now or can be considered to be an occupational disease.

“Any time we get guidance from the Supreme Court of Canada, it is going to be at the very least persuasive,” says Loretta Bouwmeester, a partner at law firm Mathews Dinsdale & Clark LLP. The Supreme Court’s decision is binding on B.C.’s workers’ compensation board for that case and those circumstances, but that still leaves a lot up in the air — not just in B.C. but throughout the rest of Canada.

So-called “presumption clauses” for occupational groups can vary by jurisdiction and affect the different types of cancers that are compensated.

Ambassador Bridge and firefighters
In their paper “Causality Advocacy: Workers’ Compensation Cases as Resources for Identifying and Preventing Diseases of Modernity” (published in New Solutions: A Journal of Environmental and Occupational Health Policy in 2018), researchers Michael Gilbertson and James Brophy discuss another case: In 2018, the Ontario Workplace Safety and Insurance Appeals Tribunal (WSIAT) rejected a case involving a female CBSA border guard who had developed breast cancer in her right breast in 2001 and her left breast in 2007.

She had worked at Ambassador Bridge for 20 years prior to her diagnosis and alleged that the cancer was linked to occupational exposures such as traffic-related air pollution, second-hand tobacco smoke and shiftwork. The researchers note that one of the central issues around the case was whether it was part of a “cluster” of breast cancer cases at Ambassador Bridge. Indeed, between 1999 and 2002, between six and eight female customs inspectors had developed breast cancers. By 2014, the cumulative total of cases was around 14 cases.

Nevertheless, WSIAT stated in its decision that evidence was insufficient to address a cluster argument and that the panel did not consider evidence of incidences of breast cancer in other workers. The panel notably found, among other things, that scientific evidence was not sufficient to support a relationship between air pollution (diesel fumes or automotive exhaust) and the worker’s breast cancer.

There are nevertheless some instances in which breast cancer is legitimately deemed to be an occupational disease. In Alberta, for example, if firefighters have a minimum number of years of regular exposure to the hazards of a fire scene (10 years) and then have primary site breast cancer, it’s presumed to be work related and workers are eligible for WCB Alberta benefits (primary site breast cancer is the stage of cancer where the breast cancer has not spread beyond the breast or the lymph nodes under the arm).

Establishing a standard of proof
With regards to the B.C. ruling cited above, Brophy says that, to him, “one of the most significant findings of the Supreme Court ruling was that essentially the compensation boards are not applying the right ‘standard of proof’ to adjudicating occupational disease claims. The standard is a ‘probable connection’ and subsequently, did the workplace play a ‘significant contributing role’ in the causation of the particular disease.”

However, he says that the compensation standard of proof is not the same as a scientific standard or even the legal standard of “beyond a reasonable doubt.”

“This is important,” says Brophy, “because the scientific evidence is quite robust regarding an association between certain carcinogens and endocrine-disrupting chemicals. However, the compensation boards do not apply the correct standard of proof and, therefore, reject claims for a ‘lack of sufficient evidence.’”

This could explain the ruling in the Ambassador Bridge case.

What can we conclude?
To summarize, this is not saying that, in every case, breast cancer is an occupational disease. Of course, breast cancer is related to other factors as mentioned previously (lifestyle, genetics, etc.).

The question here is, within certain industries, is there an explicit risk of breast cancer? And, consequently, in those industries, such as the plastics sector, can breast cancer be considered an occupational hazard?

The answer remains complicated, and the main culprit seems to be the lack of perceived scientific evidence. And it’s not just about the science — regulatory and legal bodies play a part, too.

Alhough we have discussed studies that prevent conclusive results and there is certainly evidence of carcinogens that directly correlate with breast cancer, courts may not deem current evidence to be conclusive enough.

“Occupational disease is a huge draw on resources for our health-care system, in addition to negatively impacting workplaces and harming those suffering from it and their families,” says Bouwmeester. She adds that it’s to everyone’s benefit that we better understand carcinogens in workplaces. “From a humanistic, moralistic and legalistic perspective, there’s a benefit to getting more reliable research done.”

Lack of knowledge is a huge problem for workers affected by breast cancer. A better understanding of the disease and the risks presented by certain environments and chemicals is necessary, in large part because recognition as an occupational disease means fairer and easier access to workers’ compensation.

It’s also about knowledge. A better understanding of this issue could lead to positive improvements in these industries as, ultimately, every worker has the right to a healthy and safe workplace.

Echoing McArthur’s calls at the beginning of the article, the Occupational Cancer Research Centre issued general policy recommendations to prevent occupational cancers in Canada in its September 2019 report “Burden of Occupational Cancer in Canada: Major Workplace Carcinogens and Prevention of Exposure” including strengthening occupational exposure limits, reducing or eliminating the use of cancer-causing substances in workplaces and creating registries of workplace exposures to occupational carcinogens that will help keep track of exposures over time.