The scientists analysed the circumstances of the case – heard by the Workplace Safety and Insurance Appeals Tribunal (WSIAT) – by applying the Bradford Hill criteria – a group of nine principles that are useful in establishing epidemiologic evidence of a causal relationship between a presumed cause and an observed effect. The criteria considers strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment and analogy.
The case focused on whether the woman had a genetically inherited predisposition to develop breast cancer because of dysfunctional BRCA1/2 tumour suppressor genes. It was found that her BRCA1/2 tumour suppressors were not working – but that was not connected to her inherited genes. This condition is known as “BRCAness” and is sporadic, rather than an inherited breast cancer.
The Stirling team investigated whether the dysfunction was potentially caused by occupational exposures to pollution. A review of previous research confirmed that BRCA1 can be “silenced” by exposures to dioxins and polycyclic aromatic hydrocarbons – both found in exhaust fumes.
In addition, other research has shown that BRCA2 is rapidly degraded in the presence of aldehydes – also components of exhaust fumes.
“There is much more research to be undertaken,” Dr Gilbertson said. “But we now have plausible mechanisms for inferring how the BRCA1/2 tumour suppressors in this highly-exposed border guard became dysfunctional and likely contributed to the ongoing epidemic of sporadic, early onset, premenopausal breast cancer among her colleagues.
“These outbreaks of breast cancer represent a new occupational disease that we are provisionally calling ‘occupational BRCAness’.”
The front-line workers also identified nightshift work as a potential contributing factor to their high incidence of breast cancer.
Drs Gilbertson and Brophy considered whether nightshift work might exacerbate the exposures to mammary carcinogens in traffic-related air pollution. They pointed to a previous study involving rats that found those exposed to continuous daylight developed tumours 36 per cent faster – and had 60 per cent more tumours – than those subjected to a normal photoperiod.
Significantly, the WSIAT rejected the woman’s case.
Reflecting on the findings, Dr Gilbertson continued: “Reweighing the scientific evidence using a consensus medico-legal framework – the Hill Bradford criteria – enabled us to show the amount of evidence that the WSIAT had ignored in dismissing this worker compensation case.”
He added: “This kind of forensic research depends on asking new questions based on conclusions from the existing evidence and a willingness to follow leads into unfamiliar areas of science.
“The gratifying part was to find that other scientists in other disciplines had already supplied credible answers that could then be assembled into the Hill’s framework of indicia for this specific case which can explain the clusters.”
The study, Causality advocacy: Workers’ compensation cases as resources for identifying and preventing diseases of modernity, is published in New Solutions.