Cancer clusters

Cancer clusters

March 14, 2013
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Amy Corderoy

Amy Corderoy

Health Editor, Sydney Morning Herald

Spikes in illness rates are clear. But finding a cause is never easy.

Cancer cell PULSE 7 March 2013. Digital medical illustration.<br /><br />
Cancer cell. iStock Photo    File #18235009Cancer clusters can strike fear in modern homes or workplaces, but is the panic misplaced?

They were being knocked down, one at a time. Like bowling pins, was how one described it.

When woman after woman working at the ABC’s Toowong studios in Brisbane started developing breast cancer, they knew something had to be wrong.

”It was just getting too many,” producer’s assistant Deb Ormerod told Australian Story. ”It was like six or seven cases by then, then all of a sudden, there was, like, four girls in a 12-month period, and that’s when the warning bells just went right through the roof.”

Investigators eventually found women working at the studios were six times more likely to develop breast cancer. It also seemed that the longer they worked there, the more likely they were to get sick.


The studios were abandoned in December, 2006. Many other women working at the ABC feared they, too, could fall victim to the mysterious carcinogen wrecking the lives of so many. But a strange thing happened. No amount of scanning, prodding or swabbing could find a cause; relentless testing of the studio revealed no substance to blame.

”We have to conclude that looking back on it, like most cases of cancer clusters, it was by chance,” says Professor Bruce Armstrong, who led the investigation.

Cancer clusters can strike fear in modern homes and workplaces. But is this simply misplaced panic in the face of what is eventually found to be coincidence?

Often something that seems like a cancer cluster may not even involve an increased rate of disease, says Bernard Stewart, a professor at the University of NSW and the head of the cancer control program at the South Eastern Sydney Local Health District.

”It is not possible to recognise causation of cancer in the way it was portrayed in the film Erin Brockovich, where just seeing it is the sole evidence,” he says.

”The travesty in Erin Brockovich is not that ingested chromium VI causes breast and other tumour types; the travesty is the suggestion that the impact of any environmental carcinogen could be so marked as to be self evident,” he wrote in a stinging editorial in the Internal Medicine Journal.

”Should long-held views prejudice the investigation of newly reported cancer clusters? The answer is ‘yes’,” he says.

Stewart was responding to a study that examined cancer cluster investigations for 567 sites or categories of cancer over the past 20 years. It found that in 87 per cent of cases, authorities could not even find a true increase in cancer rates, let alone a cause.

”Considered against the thousands of cancer clusters reported to authorities each year in the United States, the new data indicate that the probability of establishing causation in relation to a community-reported cancer cluster is negligible, mesothelioma clusters exempted,” Stewart says.

The problem, then, is what to do. Despite the cost and difficulty of investigating clusters, Stewart says they cannot be ignored.

”Investigations are often put in place not because the medical science says they are worthy of further scrutiny but because the people have exercised their democratic right to go to their local MP and say ‘we want this investigation’,” he says. ”What we need to do is lift the level of understanding in the whole community.”

Being told the statistics don’t support your fear can only inflame the situation.

In Toowong, many of the women were disturbed by what they saw as a lack of support and rigorous investigation.

They rejected early attempts by epidemiologists who did not actually go into the site and look for causes.

Armstrong says the women also initially rejected tests done by his investigation because some were not totally complete. Armstrong is often called on to investigate cancer clusters. He says Toowong was one of the most difficult, extensive investigations he has undertaken. It was also one of the most likely to produce a positive finding because of the real increased rate of cancers that was found.

”It was certainly one of the most thorough investigations we did,” he says. ”But the reality with cancer clusters is that the balance of them occur by chance”.

Armstrong says other medical conditions, such as heart attacks, will cluster just as frequently as cancer – it’s just that people take those conditions for granted.

Phyllis Butow, professor of psychology at the University of Sydney, is an expert in the psychological impact of disease. She says cancer brings with it a special fear. ”Data suggests people catastrophise about risks they see as life-threatening; they search for the threat, in fact, and are more likely to see it,” she says.

”There is a lot of evidence that people find cancer more scary than other diseases [with] just as high mortality rates.”.

Chance findings

There is a 95 per cent chance that one of the hundreds of suburbs in NSW will have a statistically significantly increased rate of a cancer at any given time, NSW Health says. Recent investigations, such as those into the Kooragang coal plant last year, have found the events were likely due to chance. An investigation into an apparent cluster in Helensburgh last year found no local factor that could be responsible. In 2010, an investigation into five Singleton residents who developed brain tumours also found no potential cause.

In Victoria, revelations the Country Fire Authority knew of water contamination at its training college for at least 12 years prompted the reopening of an investigation into the Fiskville cancer clusters.

In 2008, an investigation ruled out a cancer cluster at the National Gallery of Australia in Canberra.

What the US study found

+567 suspected cancer cluster sites were studied over the past 20 years.

+In 87 per cent of cases, a true increase in cancer rates could not be established, let alone a cause.

+In only 0.5 per cent of the cancer types was there some evidence of a link between the cancers of concern and the suspected carcinogen.

Source: Critical Reviews in Toxicology: Cancer clusters in the USA. What do the last 20 years of state and federal investigations tell us?

About Dr Colin Holloway

Gp interested in natural hormone treatment for men and women of all ages

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