Any consideration of cancer, be it from a preventive or curative point of view, is extremely difficult because cancer is a family of conditions, not a single disease. At present only about a third of all cancers have identifiable causes, and opinions vary as to whether all cancers will eventually be found to have an environmental, and therefore preventable, cause.
Worldwide, the six most common cancers in men are of the: lung; stomach; colon and rectum; mouth and pharynx; prostate; and oesophagus. In women the most common cancers are of the: breast; cervix; stomach; colon; rectum; lung and mouth; and pharynx. These, together with those of the brain, bladder and lymphatic tissues, and leukemia, account for three-quarters of all new malignancies. Stomach cancer is the most common cancer worldwide, closely followed by that of the lung.
The considerable variations seen from country to country, and the patterns of cancer emergence in migrant populations as they move to live in westernized countries, strongly suggest that many, if not most, cancers are linked to lifestyle and environment. Some experts claim that as many as 80-90 per cent of all cancers will eventually be preventable. Having said this, it would be easy to give the impression that only western countries have large burdens of cancer. They do not-they just have different cancer patterns.
Although the exact way in which the following are implicated in cancer causation is none too clear they have all been definitely connected with one type or another.
• Tobacco smoke.
• Alcohol and alcoholic mouthwashes.
• Obesity.
• Poor personal hygiene.
• Too much sun.
• Food additives.
• Pollution.
• Medicines and medical procedures.
• Certain infections.
• Exposure to radiation.
• Lack of vitamins, especially À, Ñ and E.
• Hot drinks and food.
• Too little dietary fibre.
• Viruses.
• Sexual behaviour.
There are, of course, many other factors involved in producing cancer but these are the main ones.
Although there are so many different types of cancer, more than 80 per cent of all cancers in men are caused by ten types. More than 75 per cent of those in women are caused by a different list of ten types. Six are common to both lists so there are only about fourteen types of cancer that are common and they cause between them four-fifths of all cancer deaths. Of these fourteen the half is sufficiently well understood to be able to give at least some preventive guidelines. Here are a few thoughts on those which are not yet preventable.
• Stomach. The incidence of stomach cancer is falling in all westernized countries for some unknown reason. It is much more common in Japan but the incidence is falling there too, probably as a result of good screening measures. Perhaps the worldwide fall in this disease has something to do with the way food is stored. An alternative explanation is that people are eating more fresh fruit and vegetables and consuming less salt.
• Prostate. There has been a twofold increase in male deaths from cancer of the prostate gland this century in England and no cause has been found.
• Brain. There has been a steady rise in the figures for brain-cancer mortality this century-perhaps due to better diagnosis. Many cases would have been missed before.
• Ovary. There is an increased risk of cancer of the ovary in women who have early first intercourse, have their first pregnancy by age 20, have few children and have an early menopause. Thus it would appear likely that the cancer is linked to hormonal changes in some way.
• Breast. This, the biggest cancer killer in women, is still not preventable.
• Rectum and large bowel. Dietary factors are suggested but no single one is definitely the cause.
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