Cancer 'epidemic' isn't happening

By JOE SCHWARCZ, Freelance May 16, 2010 5:05 AM

Ladies who work with the fabrics used to produce those colourful little ribbons that have become the symbol of the fight against breast cancer might consider increasing their broccoli consumption. Why? Because the ribbons may actually be causing the feared disease. Broccoli, on the other hand, could offer protection.

The problem isn’t wearing the ribbons. It’s making them – particularly if they are made from nylon or acrylic fibres. At least, that’s what a study headed by France Labrèche of the Université de Montréal and Mark Goldberg of McGill University suggests.

Labrèche and Goldberg compared more than 500 post-menopausal women who had breast cancer with a similar number suffering from other cancers. All the women were carefully questioned about their lifestyle and occupational history. (Such “case-control” studies are commonly used to detect possible associations between environ- mental factors and disease, but they cannot prove cause and effect.) This particular study revealed for every decade a woman was exposed to acrylic fibres, as can happen in a textile mill, her risk of being found to have breast cancer was increased eight fold. Exposure to nylon fibres doubled the risk.

Does this make any sense? Possibly. Dyes, flame retardants or residuals of the chemicals used to make the synthetic fibres could be the culprits. Or not. People’s memories of events that occurred decades earlier are notoriously unreliable.

Maybe the women who worked with fabrics had more nighttime shifts. Studies of animals have suggested that disturbances in the light-dark cycle can alter the levels of such hormones as melatonin or estrogen in such a way as to increase the risk of breast cancer. Epidemiological studies of humans, particularly of nurses and flight attendants, also have shown night-shift work may increase the risk of breast cancer.

The Danish government found these studies so convincing that it granted breast cancer the status of an occupational disease and now offers compensation to affected women who have no other obvious risk factors.

If your night and day shifts happen to be in China, however, there’s no need to worry. A U.S. National Cancer Institute study of 70,000 women in Shanghai found no association between shift work and breast cancer, even among women who had more than 25 years of such work. Of course, the Chinese women may have genetic differences, or may have a diet that features far more plant products than the usual Western fare.

Which brings us to the broccoli issue. Research suggests breast cancer is initiated by the growth of cancer stem cells that continuously renew and change into different cell types. These stem cells are believed to be involved in cancer relapse as well as in resistance to treatment.

University of Michigan researchers have found bathing breast cancer stem cells in a solution of sulphoraphane, a compound found in broccoli, inhibited the cells’ growth. They then implanted cancer cells into the mammary glands of mice and injected the animals with sulphoraphane on a daily basis. Subsequent examination of the tumours revealed the breast cancer stem cells had been eliminated. Furthermore, when living cancer cells extracted from the sulphoraphane-treated animals were implanted into a secondary group of mice, there was no tumour growth.

Pretty impressive, but we cannot assume applying sulphoraphane to cancer cells under controlled conditions is comparable to eating broccoli.

Still, sulphoraphane is only one of a myriad of plant-based compounds that have excited researchers with their anti-cancer properties and driven consumers into the fruit and vegetable aisles.

Alas, just as we’re learning to pile all those vegetables and fruits on our plate, a study appears in the Journal of the National Cancer Institute telling us that an apple a day may not keep the doctor away, after all. An analysis of the diets of more than 400,000 people showed increasing fruit and vegetable intake to five servings a day reduced the risk of cancer by only a few percentage points – nothing like the 30 to 50 per cent that nutritional authorities have bandied about.

Some argue pesticide residues on the fruits and vegetables may be negating the protective effect, but while there is plenty of evidence of pesticides causing harm in an occupational setting, trace residues on food are a different matter. Plants produce far more natural pesticides to protect themselves than the man-made residues they may harbour.

But if you repeat something often enough, it becomes true just by repetition. Keep saying that pesticide residues and traces of other chemicals in our environment are responsible for the cancer epidemic, and it becomes the “truth.” Well, the truth is that there is no cancer epidemic. The National Cancer Institute compiles excellent data on cancer incidence, treatment and mortality. Contrary to popular perception, the overall cancer incidence is declining. Breast, prostate, colon and uterine cancer rates are falling but, unfortunately, pancreatic, thyroid, testicular and childhood cancers are rising. In all cases, however, the changes are very small.

Why do I discuss all this? Because the President’s Cancer Panel in the U.S. has just come out with a report suggesting the number of cancer cases caused by environmental exposure has been “grossly underestimated.” There is the usual reference to the 80,000 chemicals in commercial use, “of which only a few hundred have been tested for safety.” Actually, only about 3,000 of these are high-volume chemicals, and safety information on these is available to anyone who cares to look up the material safety data sheets.

True, the information does not encompass the effects of trace exposure, for the simple reason that this is close to impossible to determine. Of course, one can and should always ask for more safety data, and “high-throughput screening technologies” are being developed to test many chemical effects simultaneously.

But as I have tried to show, cancer is a multifactorial, complex disease, and the notion that exposure to trace amounts of chemicals is a major cause is more conjecture than fact.

Joe Schwarcz is director of McGill University’s Office

for Science and Society (www.OSS.McGill.ca).

He can be heard every Sunday from 3-4 p.m. on CJAD radio. joe.schwarcz@mcgill.ca
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