Page: 37
Decision No. 1642/21
laboratory technicians to potentially carcinogenic substances. They confirmed that the
number of diagnoses of breast cancer (7 of the 63 workers studied were so diagnosed)
represented a statistically significant cluster, with a “standardized incidence ratio” for
breast cancer approximately eight times the rate that would have been expected in the
general population. As to potential causes, the authors of these reports observed no
current occupational chemical exposures, but noted that past exposures were “likely
much higher”, and included one known human carcinogen (Final Report, at p. 35).
[134]
As noted, the decision referred to the group of breast cancer cases as a “cluster”. It is
implicit in the decision that this cluster of breast cancer cases occurred contemporaneously. The
decision of the British Columbia Court of Appeal, (Fraser Health Authority v. Workers
Compensation Appeals Tribunal, 2013 BCSC 524) which was the subject of the appeal to the
S.C.C. noted that:
Cluster research has shown that elevated rates occur by chance at some geographic
locations and times. In fact, clusters always occur and it is a statistical phenomenon -
even when there is no causal factor that is responsible for the increased incidence (this is
why so few cluster investigations uncover any new risk factors). So, if we look around at
many geographic areas and times we will find some clusters; if a specific cluster is
related to statistics and not an etiologic agent, it is most likely that in the next time period
at this location the rate will not be significantly elevated…[emphasis added]
[135]
The majority S.C.C. decision concluded that, in cases where there is a lack of evidence
supporting the cause of the cancers, other evidence, such as the circumstantial evidence provided
by the fact that the cancers occurred at the same employment location and at contemporaneous
times, might nevertheless provide the basis of a finding that the cancers were occupationally
related. The decision stated, at paragraphs 38 and 39:
The presence or absence of opinion evidence from an expert positing (or refuting) a
causal link is not, therefore, determinative of causation (e.g. Snell, at pp. 330 and 335). It
is open to a trier of fact to consider, as this Tribunal considered, other evidence in
determining whether it supported an inference that the workers’ breast cancers were
caused by their employment. This goes to the chambers judge’s reliance upon the Court
of Appeal’s decisions in Sam and Moore and to Goepel J.A.’s statement that there must
be “positive evidence” linking their breast cancers to workplace conditions. Howsoever
“positive evidence” was intended to be understood in those decisions, it should not
obscure the fact that causation can be inferred – even in the face of inconclusive or
contrary expert evidence – from other evidence, including merely circumstantial
evidence. This does not mean that evidence of relevant historical exposures followed by a
statistically significant cluster of cases will, on its own, always suffice to support a
finding that a worker’s breast cancer was caused by an occupational disease. It does
mean, however, that it may suffice. Whether or not it does so depends on how the trier of
fact, in the exercise of his or her own judgment, chooses to weigh the evidence. And, I
reiterate: Subject to the applicable standard of review, that task of weighing evidence
rests with the trier of fact — in this case, with the Tribunal.
In light of the foregoing, the Tribunal’s original decision cannot be said to have been
“patently unreasonable”. While the record on which that decision was based did not
include confirmatory expert evidence, the Tribunal nonetheless relied upon other
evidence which, viewed reasonably, was capable of supporting its finding of a causal link
between the workers’ breast cancers and workplace conditions.
[136]
I have considered the S.C.C. decision in the context of this appeal and I find that the
S.C.C. decision should be distinguished from this appeal on its facts. In the case which was the
subject of the S.C.C. decision, seven of 63 people studied, who worked at the same hospital lab,
at about the same time, were diagnosed with breast cancer. In this case, information has been