|The Causes of Cancer|
|Each year in the United Kingdom more than 230,000 persons die of cancer. One in three of all persons born in the United Kingdom develops some form of cancer during his or her lifetime. The suffering of patients and the heartache of family and friends represent a tragic social cost. The agony of patients who develop the disease when their children are growing up represents an intolerable burden.
Cancer is not one disease. It is a hundred or more diseases. It can be induced in experimental animals by the use of chemicals, radiations or viruses.
Inspired by the success with antibiotics in controlling infectious diseases, the public,and indeed cancer research scientists have been concentrating in seeking a cure. It is just possible that for many of the forms of cancer there will be no magic cure and the most practical approach will be to find means of prevention and of prophylaxis
Certain occupations carry a higher risk of cancer development compared to the rest of the population. Cancer of the bladder is associated with rubber, dyestuffs and electric cable industry workers; cancer of the lungs is associated with uranium mining as indeed it is with cigarette smoking; leukaemia is associated with excess exposure to ionizing radiations; cancer of the mesothelium, ( tissue lining the lungs), is associated with asbestos workers and miners; liver cancer is associated with vinyl chloride workers.
Many specialists in the field of cancer research now believe that chemicals present in food and the environment in general are responsible for 80 to 90 per cent of all cancer in humans; the remainder are believed to be caused by radiations or viruses. Current evidence suggests that there exists no safe threshold level for a carcinogenic chemical. Aflatoxin, a natural product and a human food contaminant, can be detected analytically down to levels of one part per billion (ppb). It produces one hundred per cent incidence of cancer in rats when incorporated in their diet at levels of 15 ppb. Our knowledge of the action of chemical carcinogens indicates that they act optimally when administered as frequent small doses over a period of time rather than as large single doses.
There are basically two major classes of environmental carcinogens; the potent carcinogens such as the aflatoxins and nitrosamines, which can produce cancer in laboratory animals even in the very low concentrations which have been found in food; there are also the weak carcinogens such as atmospheric pollutants, a number of pesticides and food additives, with effects that may easily escape detection by conventional biological tests. Because such weak carcinogens are unlikely to be implicated epidemiologically, they may be as dangerous, or possibly more dangerous than the more obvious potent carcinogens.
|There is long latent period between exposure to a carcinogenic chemical and the clinical appearance of cancer. There are instances of persons who had been born in the vicinity of asbestos mines and left the area in early childhood, developing mesothelioma in their fifties and sixties. A few years ago a rare type of vaginal cancer was observed in young women, who twenty years previously have been exposed to a synthetic female sex hormone, diethyl stilboestrol, (DES), as foetuses when their mothers were treated with the drug. The recent rise in childhood leukaemia is attributed to prenatal exposure to endocrine disrupting chemicals such as pesticides or petrol additives that program the developing foetuses for cancer in early life. There is a fundamental difference between a developing system such as the foetus and a mature system. If one starts giving a synthetic female sex hormone, DES to a month-old mouse and continues throughout its lifetime one never gets any effect. But if DES is given to a pregnant mouse or human, it alters gene expression in the foetus permanently, and causes cancer or other abnormalities in the reproductive tract of the offspring. Adverse effects such as leukaemia in the offspring can be produced by the very small doses of some chemicals if they are given at a critical time during pregnancy.
There appears to be additive, cumulative and synergistic effects of combined exposures to environmental contaminants. There is evidence suggesting that smoking enhances the carcinogenic effects of asbestos.
Recent technological developments have introduced into food and the environment in general a variety of chemical pollutants whose impact upon the entire population is subtle and unpredictable. These are chemicals to which man has not been evolutionarily exposed and the effects of such pollutants in terms of cancer induction may not become apparent for thirty or more years; unless we act now the future will be bleak.
Most of us have been brought up on a cure-orientated climate. It is time to respond to the challenge of the climate of change, a challenge that demands a serious response from the government as well as from industry and the public.
That is why the Cancer Prevention Research Trust is launching this unique initiative. Preventing cancer is a serious business for all of us.