Is cancer more common today than it was in the past?
Each year, more and more people are diagnosed with cancer in the western world. For example, in Finland there were 8000 new cancer cases diagnosed per year at the time when the Finnish Cancer Registry was started in the beginning of the 1950s. In 2007, there were about 27 000 new cancers. One could well say that cancer is exploding. Similar trends are seen in other countries, where ever there are good statistics. There are over 3 million new cancers diagnosed in Europe every year. There is, however, an important point to be noted. The risk of cancer increases with age, and the disease is most uncommon in people younger than 40 years of age. By the age of 85, every third person will have been diagnosed with a cancer of some type.
Therefore cancer was rare as long as average age of the population was 20 to 30 years, as was still the case, especially in lower social classes, in the 1800s. The more old people there are in a population, the more common one will find cases of cancer. This is not a “real increase”; one is dealing with competing causes of death. If a person does not die from a competing cause such as smallpox, tuberculosis or pneumonia, he or she has a high possibility of contracting cancer by the age of 70 or 80 years.
Cancer at different times can only be compared, if age-standardisation is done with the numbers. The incidence of cancer is calculated separately for each age group. If we want to compare cancer incidences for two years, say 1950 and 2000, we can calculate the standardised incidence in 1950 assuming the age structure of the population of the year 2000. Then both years will be comparable. In international comparisons, it is customary to use the average age structure of the whole world. Thus it is possible to compare cancer incidences in different countries even though the age structure would be different in the various countries. This is the case between industrial countries and developing countries.
In Finnish men, the age standardised total cancer incidence has increased moderately over the last years. On the other hand, there have been major changes in the individual cancers. Prostate cancer, intestinal cancers, kidney cancer, bladder cancer and melanoma have increased clearly. In contrast, stomach cancer, oesophageal cancer, laryngeal cancer and lip cancer have clearly decreased. Lung cancer increased until the 1970s, thereafter it has decreased.
Why do we have these changes? All causes are not known, but we have a number of hints at the reasons. Prostate cancer and intestinal cancers belong to the so-called “affluence cancers”, they are more common in more affluent social groups. One of the explanations could be the diet, but at least the “increase” of prostate cancer is in part explained by improved diagnostics. Melanoma is clearly associated with sunbathing and sunburns and it is therefore a “holiday cancer”. Lung cancer increases with about a 20 year delay from the time an individual starts to smoke cigarettes, but the risk decreases already within a few years after quitting. Smoking among males has decreased in northern Europe since the 1960s. Kidney and bladder cancers could in some way be related to occupational chemicals, but they are also associated with smoking. The decrease of stomach cancer may have something to do with improved food safety, food keeps better, and we are less exposed to mould toxins. In addition, heavily salted and smoked food items are no longer so popular as they were in the days of our grandparents.
The total cancer incidence of women has increased during the past 50 years by over 50%, from about 150 to almost 250 cancers diagnosed yearly among 100,000 women (age standardised). The most important individual cancer responsible for this increase is breast cancer. Other more common cancers include intestinal cancers, lung cancer and melanoma. The incidences of stomach cancer, cervical cancer of uterus and oesophageal cancer have decreased clearly.
Breast cancer associates with giving birth to fewer children than before, earlier sexual maturation but delayed time before having the first baby, and later menopause, and in addition, with overweight and decreased exercise. With respect to lung cancer, an interesting development has taken place: it was initially a disease of the upper social classes, but this changed in the 1980s to becoming a disease of the lower classes. This follows the development of female smoking: cigarette smoking was initially predominantly a habit of upper class women, but once the dangers were realised, the popularity of smoking by this better educated population rapidly waned. Today, both male and female smoking as well as lung cancers are more common in the lower, less educated, social classes.
Female melanoma is associated with sunbathing and sunburns in the same way as in men. It is worrying that melanoma and a few other cancers have increased most in the younger age classes. In women born in the 1950s, melanoma was as common at 35 years of age as it used to be at 70 years of age in women born at the beginning of the 20th century. Thus melanoma not only has become more common, but women are also falling prey to this disease at a much younger age.
Cancer deaths are decreasing in most countries. The most common cause of death in Europe in 2006 was lung cancer which accounted for one fifth of the total number of cancer deaths. Nonetheless, the death toll is formidable – lung cancer kills more than 300,000 Europeans every year.
The numbers of cancers have increased, but this largely is due to our aging population. A few cancers seem to have increased even when age correction is applied. The most obvious cancers whose increase could be stopped are skin melanoma and female lung cancer.
Notes and references
- Incidence means the number of new cases per time unit, usually per year.
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