Cancer: A Modern Epidemic?

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Cancer is a serious health worry for most of us. Now that we rarely die of infectious diseases, heart disease and cancer are two of the main causes of death. Has modern Western society produced a ‘cancer epidemic’? No! Although lung cancer is increasing, particularly in women, is there any doubt that this increase is entirely from cigarettes? It generally takes two decades of puffing before lung cancer catches up with smokers. Until a few decades ago, women smoked less than men, so only recently have women joined the inmates of lung cancer wards. Maori women, who traditionally have had some of the highest smoking rates in the world, were already well represented in the lung cancer statistics.

Even after lung cancer is excluded from the figures, it’s true that more people are dying of cancer than a century ago. There’s no surprise about that. Now that many formerly lethal infections can be cured or prevented, people are living longer than a century ago, since. Cancer is for the most part a disease of older people. Medical researchers have mathematical ways to adjust for age- ­related risks. Without such adjustment, raw numbers can be misleading. How can you compare, for instance, the rates of prostate cancer (a disease of older men) in two countries, one of which has half its population under the age of 13, and the other with most citizens over 50? The answer is that the observed numbers, grouped by age, are adjusted to fit idealized populations with the same theoretical distribution of age groups. When this straightforward adjustment is done, the so-called ‘epidemic of cancer’ disappears! Since cancer is not a single disease but a group of diseases, overall cancer rates don’t mean much. There have been shifts in types of cancer, both up and down. Stomach cancer is now less common than before, perhaps because of better food hygiene. Female breast cancer rates have increased slightly, perhaps because deaths in childbirth have dropped.

There are some types of cancer that seem to have increased, particularly childhood leukaemia. There has been considerable debate in the medical literature about how much of this is caused by better detection and diagnosis. After all, many such deaths in the past have been ascribed to some vague malicious influence of ‘unhealthy air’. Dr Martha S. Linet of the National Cancer Institute reported a steady decline in death rates from all major types of childhood cancers (including leukemia) in the years between 1975 and 1995. The death of children from any cause is tragic, and concentrating just on cancer can be counterproductive.