Expert evidence found no definitive causation but couldn’t rule it out either
The Supreme Court of Canada has ruled that breast cancer in three British Columbia workers who worked in a medical lab should be considered an occupational disease entitling them to workers’ compensation, overturning a lower court decision and reinstating a tribunal decision.
Katrina Hammer, Patricia Schmidt, and Anne MacFarlane, all in their 50s, were technicians in a hospital lab for the Fraser Health Authority in Vancouver. Their jobs involved testing blood and other bodily substances using chemicals such as falmalin, a component of formaldehyde.
All three women were diagnosed with breast cancer, as well as four other technicians at the same hospital lab. Six of the cases were diagnosed between 2000 and 2005.
Hammer, Schmidt and MacFarlane all applied for workers’ compensation on the basis that their breast cancer was an occupational disease, given the number of cases in the same workplace. It was also known that some of the chemicals they used were potentially carcinogens.
However, a Workers’ Compensation Board review officer denied all three of the claims, finding there was insufficient evidence that the breast cancer was related to their jobs. The workers appealed to the B.C. Workers’ Compensation Appeal Tribunal, which overturned the review officer’s decision and found the workers’ breast cancer to be occupational diseases. Though the tribunal acknowledged the need for “positive evidence linking the disease to employment,” it found that without evidence specifically disproving a link, common sense should prevail in inferring that it was possible. It wasn’t necessary to identify a specific cause of the breast cancer if the evidence pointed to a causal link — and the likelihood of past carcinogenic exposure along with the “statistically significant cluster” of breast cancer in the lab workers, made it “as likely as not” that the breast cancer was caused by workplace exposure, said the tribunal.
The Fraser Health Authority appealed to the tribunal for reconsideration, but was unsuccessful as the tribunal upheld its initial decision. Unfortunately for the workers, they were not to get their compensation yet, as the health authority appealed to the B.C. Supreme Court for judicial review of the tribunal’s decision.
Court finds no link between workers’ cancer and work
The provincial Supreme Court found that the tribunal erred in finding a causal link between the workers’ breast cancers and their employment. The court based its decision on the B.C. Workers’ Compensation Act and a report by the Occupational Health and Safety Agency for Healthcare in British Columbia (OHSAH).
The act stipulated that it was designed to favour the worker, so if the evidence was evenly weighted on whether a disease was caused by employment or by non-employment causes, the decision should be in favour of compensation for the worker. However, the OHSAH report, which was published in March 2006 and looked at the higher incidence of breast cancer cases at the lab, found the seven cases of breast cancer at the lab was “a statistically significant cluster” — eight times the rate expected in the general population — but couldn’t conclude there was a link between the disease and work-related exposures. Though it couldn’t find a link, it didn’t rule out the workers’ employment as a possible cause either.
The report reviewed scientific literature on breast cancer risk factors, analyzed the cluster of cancer cases at the lab, and investigated possible exposure to carcinogens. It speculated that the increased breast cancer rate among lab employees could be due to “(1) a cluster of reproductive and other known, non-occupational, risk factors; (2) past exposures to chemical carcinogens and less likely to ionizing radiation; and (3) a statistical anomaly.”
The OHSAH report was backed up by two doctors — a specialist in occupational medicine and a medical advisor to the Workers’ Compensation Board, also specializing in occupational medicine. Both doctors agreed there was a lack of scientific evidence to link the workers’ breast cancer to their employment, with one of them saying he “would prefer to refute than support” that link.
The B.C. Supreme Court found the tribunal “was not entitled to ignore the expert evidence in favour of its own expertise or common sense, and it was patently unreasonable to do so.” OHSAH and two specialists “clearly and unambiguously concluded that there was no evidence that workplace factors caused the workers’ breast cancers,” and there was no evidence to the contrary, said the court.
Possibility of causation not ruled out: Supreme Court
The workers took their case before Canada’s top court, which agreed to hear the appeal. The Supreme Court of Canada noted that the tribunal’s decision in favour of the workers was a finding of fact, so the basis of proof was determining whether the evidence was capable of supporting that finding, not conclusively demonstrating it. Like the tribunal, the court also noted the standard of “causative significance” meant there only had to be the possibility of a link, which was a different standard of proof than that of the reports by OHSAH and the doctors. As a result, relying completely on the reports’ conclusions on a causal link was inappropriate and an error on the part of the lower court, said the Supreme Court.
The top court found that it was undisputed that the OHSAH report, supported by the two doctors’ reports, determined there was a statistically significant cluster of breast cancer among the lab workers which was much higher than the rate in the general population. In addition, the report noted there was the possibility of higher chemical exposures in the past. Though they were unable to reach the scientific conclusion to support a link between the breast cancer and work-related exposures, OHSAH only speculated it was the result of non-occupational factors — there was no conclusion on this, said the court.
The Supreme Court of Canada pointed out the tribunal correctly stated that the reports didn’t exclude the possibility of occupational causation, leading it to find that the likelihood of the incidence of cancer being simply a statistical anomaly didn’t exceed the likelihood that the workers’ breast cancers were an occupational disease caused by their employment.
Though the B.C. Supreme Court found the tribunal should not have ignored the expert evidence in favour of its own expertise, the Supreme Court of Canada disagreed, saying it “was precisely the sort of issue that the legislature intended that (the tribunal) should decide” as the act gave the tribunal exclusive jurisdiction to determine fact from inferences based on the evidence it had. In this case, the tribunal heard evidence of possible exposures in the past and a statistically significant cluster of breast cancer cases among lab workers. This could be considered evenly-weighted evidence with the OHSAH reports — which was not definitive positive evidence ruling out work-related causation — leaving the tribunal the ability to find in favour of the workers, said the top court.
“The presence or absence of opinion evidence from an expert positing (or refuting) a causal link is not, therefore, determinative of causation,” said the court. “It is open to the trier of fact to consider, as the tribunal considered, other evidence in determining whether it supported an inference that the workers’ breast cancers were caused by their employment.”
The Supreme Court of Canada — in a six-to-one decision — found the tribunal’s original decision entitling the three workers to compensation for work-related breast cancer was reasonable and weighed all the evidence. It allowed the workers’ appeal with costs, restoring the tribunal’s decision.
The one dissenting judge, Justice Suzanne Cote, found that there was a lack of positive evidence of causation and the expert reports swayed the evidence in favour of no link, rather than being evenly-weighted. Using the cluster of cases as a basis for causation was “mere speculation,” said Cote.
For more information see:• British Columbia (Workers’ Compensation Appeal Tribunal) v. Fraser Health Authority, 2016 SCC 25 (S.C.C.).