Alarming rates of cancer in pets and wildlife offer clues to human cancers : Studies show chemical contaminants may disrupt thyroid function, cause breast cancers and taint placental blood and fetal development

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In May 2007, the American Cancer Society’s Journal Cancer published a database identifying 216 chemicals that are known to cause breast cancer in animals. Many of the same chemicals are also present in consumer products, food contaminants, air pollutants and in our places of work.

Until recently it was widely believed that cancer was caused mostly by our lifestyle and dietary choices, with a little bit of hereditary bad luck thrown in. It is not only humans who are getting cancer, however. The evidence of cancer in the animal realm is one of many factors fuelling a sea-change in public thinking about the causes of cancer.

Beluga whales have lived in the world’s northern waters for millions of years, eating octopus, crabs and fish. In the Saint Lawrence estuary, however, the belugas have also been getting cancer, and yet they don’t drink, smoke, eat junk food or lie in the midday sun. Until recently, when the water pollution that was causing their cancers was cleaned up a bit, their death rate from cancer (one in four) was the same as it is among Canada’s humans. They are also having trouble reproducing – as many humans are.

When scientists looked for cancer among belugas that swim in the open Arctic waters, however, they found none. So what’s happening? The beluga autopsies revealed high levels of polycyclic aromatic hydrocarbons, a known carcinogen which most likely came from an upstream aluminum smelter.

It’s not just the whales. In Washington DC, four blocks from the White House, the Registry of Tumors in Lower Animals has almost 4,000 specimens of cancer in fish, amphibians, reptiles and invertebrates that have been collected by the Smithsonian and the National Cancer Institute.

Epidemics of liver cancer have been found in 16 species of fish in 25 different polluted locations, both fresh and salt water. The same tumors have been found in bottom-feeding fish in industrialized and urbanized areas along Canada’s Atlantic and Pacific coasts. In Canada’s non-polluted waters, cancer in fish is almost non-existent.

And then there is the disturbing evidence of cancer in dogs. A 1989 study of more than 8,000 dogs showed that canine bladder cancer was associated with their living in industrialized countries, mimicking the distribution of bladder cancer among humans.

Between 1975 and 1995, the incidence of bladder cancer in dogs examined at veterinary teaching schools in North America increased six-fold. Scottish terriers, Shetland sheepdogs, wirehaired fox terriers and West Highland white terriers all had a higher risk than mixed breeds, suggesting a genetic susceptibility to cancer among the terriers, but not a reason for the increase.

When researchers interviewed the owners of Scottish terriers with bladder cancer, they found that dogs whose owners had used phenoxy acid herbicides on their lawns were four to seven times more likely to have cancer than dogs whose owners had not. Phenoxy acid is an active ingredient in 2, 4-D, a widely used herbicide that has been linked to various cancers.

The “cancer in dogs” studies reveal the multi-factorial nature of cancer. Bladder cancer in dogs is linked to the use of insecticidal flea and tick dips, but more so if the dogs were obese and lived near another source of pesticides. Dietary protection is important, too. In the terrier study, the researchers found that when the Scotties ate green leafy vegetables three times a week, there was a 90% reduction in their risk of cancer.

Birds very rarely get cancer, but in recent years herring gulls in the polluted waters of the Great Lakes have been getting cancer, demonstrating the same multi-step model of carcinogenesis that is apparent among humans. Research shows clearly that the waters contain chemical pollutants that are known carcinogens.

How far do we need to look when seeking cause and effect? The same pattern of cancer has shown up among California’s sea lions in coastal waters where persistent organic pollutants were dumped in the 1960s and ’70s. One in five of the sea lions has cancer of the urinary or genital tract; they also have toxic chemicals in their blubber that has accumulated through the anchovies, squid, salmon and mussels they eat.

We humans are being exposed to the same body burden of toxic contaminants that is producing cancer in animals and fish. What makes us think we are immune to their effect or that our cancers are caused by lifestyle choices?

DDT is a good case in point. For years, people who have suspected a link between DDT and breast cancer have been stymied because evidence of a connection was not forthcoming. When the authors of a recent study in Environmental Health Perspectives searched for evidence of DDT contamination during the critical years of childhood and early puberty, however, they found striking evidence that girls who were exposed to high levels of DDT before the age of 14 had a five times higher risk of getting breast cancer than those who were not exposed. They also found that those who were exposed at the youngest age had the highest breast cancer risk.

Another recent study, this time from Spain, found levels of the fire retardant chemical PBDE in the placental blood of new born babies as high as that found in the blood of electronics recycling workers. PBDEs are known to disrupt thyroid function and impair development in animal studies, and there may or may not be a link to cancer. Until studies are done that look at the impact of chemicals such as this in fetal exposure and during early puberty, when the rapidly flowing hormonal messages can easily be disturbed by a rogue chemical, we will not know, and the danger will continue.

This makes it all the more disturbing that when the Canadian Cancer Research Alliance did a recent analysis into the $500 million a year that Canada spends on cancer research, they found that only 2% of the funds went into fundamental prevention, compared to 22% on improving treatment and 56% on scientific research into the biology of cancer, in the search for a cure.

Just think what we could achieve if not 2% but 20% of the funds ($100 million a year) was used to pursue preventative research to nail down the multiple ways in which chemical pollutants contribute to cancer, and lead to a clear agenda to substitute and eliminate the culprits.

Until Canada develops a strong and urgent commitment to remove the pollutants from our waters, air and food, and from the drugs, cosmetics and cleaning products that people use, we may be fooling ourselves if we expect the incidence of cancer to fall.

Go on searching for a pharmaceutical cure, by all means. But it also makes sense to observe what is happening to the animals and fish and make urgent moves to prevent cancer – both in animal and human populations, by removing the carcinogens that are known to cause cancer.

Guy Dauncey is co-author with Liz Armstrong and Anne Wordsworth of Cancer: 101 Solutions to a Preventable Epidemic (New Society Publishers, 2007)  available at: www.earthfuture.com/cancer.  He is also the Co-Chair of Prevent Cancer Now www.preventcancernow.ca.

Michael Gilbertson has worked with the Canadian federal government monitoring and regulating persistent toxic substances for 34 years, including 16 years with the International Joint Commission.  He is a member of Cancer Care Ontario’s Cancer 2020: Cancer and the Environment Stakeholder Group.