Prevention is always better than cure, particularly for diseases like cancer where treatment can be both difficult and unpleasant. But first, doctors must discover the causes so people know how to avoid ill-health. This is the primary role of epidemiology - the study of disease in human populations. Tragically, a preference for laboratory research and animal experiments diverted attention from epidemiology, and for decades little was known about the main causes of human cancer.
Before World War I, epidemiology had identified several causes of the disease.(1) For instance, pipe smokers were more likely to develop cancer of the lip; workers in the aniline dye industry often contracted bladder cancer; and skin cancer was an occupational hazard of radiologists. It was also known that combustion products of coal (soot and tar) could cause the disease, an observation dating back to 1775 when the English surgeon Potts identified soot as a carcinogen in chimney sweeps.
Attempts to replicate Potts' findings in laboratory animals repeatedly failed (2) but finally, in 1918, Japanese researchers reported that cancer could be produced on a rabbit's ear by continually painting it with tar, a discovery that changed the course of cancer research. According to the renowned British epidemiologist Sir Richard Doll, human observational data were now commonly dismissed because it was confidentally assumed that laboratory experiments held the key to success.(1) Crucial epidemiological studies like those of Percy Stocks at London University, who reported in 1933 that people consuming larger amounts of fruit and vegetables were less likely to develop cancer,(3) received little attention,1 yet today we know that Stocks was right.(4)
The absence of human epidemiological data allowed mistaken ideas based on animal research to flourish. Although we now know that only about 5% of Western cancers are linked to viral infection,(5) some scientists believed that most, if not all cases vvere caused by viruses, a view derived from experiments on animals where it is easy to transmit the disease in this way.6 One animal researcher even argued that women should not breast feed their babies: he believed that in humans, as in mice, a virus is the prime cause of breast cancer, and that the virus is acquired in the mother's milk!(7)
Following World War II, interest in epidemiology was reawakened with the striking discovery that smoking causes lung cancer. This breakthrough led to further population studies which identified the causes of many other types of cancer. The result is that 80-90% of cases are now considered potentially preventable. And it is revealing that the 1980 US Congress Office of Technology Assessment Report on the causes of cancer, relied far more on epidemiology than laboratory tests because these "cannot provide reliable risk assessments".(5)
1) R Doll, Cancer, 1980. vol.45 2475-2485
2) W.H.Woglom, Archives of Pathology, 1926 vol 2. 533-576
3) P Stocks & M.N Karn, Annals of Eugenics, 1933, vol 5, 237-280.
4) J.Robbins, Diet for a New America (Stillpoint. 1987).
5) R.Peto & R.Doll The Causes of Cancer (Oxford University Press, 1981).
6) E Northrup, Science Looks at Smoking (Conard-McCann, 1957).
7) J.Furth, Bulletin of the New York Academy of Medicine, 1964, vol.40,421-431.
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