Prediction of Cancer Incidence in the Nordic Countries up to the year 2020


Bjørn Møller, Harald Fekjær, Timo Hakulinen, Laufey Tryggvadóttir, Hans H. Storm,Mats Talbäck and Tor Haldorsen

Introduction

The five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden) are geographically, historically, culturally and politically related, and their languages, except Finnish, belong to the same group.


Political collaboration between the Nordic countries has a long history, and in 1989, a Nordic action plan was adopted by the Nordic Council of Ministers. The first part of this action plan was to acquire a complete description and analysis of cancer patterns in the Nordic countries, including predictions of cancer incidence up to the years 2000 and 2010. The Association of the Nordic Cancer Registries (ANCR) was requested to conduct this analysis, and in 1993, “Predictions of cancer incidence in the Nordic countries up to the years 2000 and 2010” by Engeland et al. (1993) was published, as the first in a series of publications about the cancer picture in theNordic countries.

 

  

Cancer of the Lung

For all the Nordic countries combined, the average annual numbers of new cases in 1993-1997 were 6702 for males and 3495 for females, comprising 13.2% and 6.7% of all male and female cancer cases, respectively (Table 12). 

This makes lung cancer the third most common cancer for women and second for men. The median ages of patients in the last observation period were 70 years for men and 68 years for women. The incidence rates increased with age at diagnosis to 348 per 100 000 person-years in males (75-79 years of age) and 112 in females (70-74 years of age) (Figure 33). 

 


   

Up to the age of 50 years, males and females had similar rates. After this, the male:female ratio of rates increased with age, to about 4.0. The trends in lung cancer have changed dramatically during the last 35 years, in both males and females, although the patterns have differed. In general, rates in males have peaked for all countries but Norway (Figure 34 top).
 

Underlying cohort-specific risks in each country reveal further details of the picture. In 1968-1972, Finland was the first of the Nordic countries to reach its historical peak. Cohort-specific risks increased for cohorts born up to around 1903, and have decreased for all subsequent cohorts. In Sweden, the peak in incidence was reached in 1978-1982. Cohort-specific rates went both up and down for different cohorts born before 1928, but risks have steadily decreased for subsequent cohorts. 


 

 

The Danish and Icelandic patterns are similar to the Swedish. The highest incidence rates were observed in 1983-1987, and cohort-specific risks started to decline for cohorts born around 1928 in Denmark and around 1932 in Iceland. The cohort-specific decline was less pronounced for Iceland. 
 

The Norwegian rates have not yet turned downwards, but are predicted to peak in the period 1998-2002. The cohort-specific pattern in Norway is different from those in the other countries. Risks steadily increased for cohorts born up to 1928, but instead of starting to decrease for cohorts born after this point, they have stabilized. Lung cancer incidence rates for males in all the Nordic countries are predicted to decrease. 
 

The rate among Finnish males is already lower than in Danish males, and is predicted to be lower than both the Icelandic and the Norwegian rates by 2003-2007. For all the Nordic countries combined, the rates will decrease by 24% from 1993-1997 to 2018-2022. The number of new cases will decrease from around 6700 annual cases in 1993-1997 to around 6500 in 2003-2007 (Table 12 top). 

 


  

By 2018-2022, the annual number of cases is predicted to be nearly 7500 per year, due to the ageing of the population. For females, the incidence rates have increased in all the countries (Figure 34 bottom). The highest levels are seen in Denmark and Iceland, and the most rapid increases have occurred in Denmark and Norway.
 

The cohort-specific risks have steadily increased for all countries, so the predicted levelling off of the rates after 2010 is a result of the assumption in the model that current trends will fade over time. For all the Nordic countries combined, the rates will increase by 26% from 1993-1997 to 2018-2022, whereas the annual number of new cases will increase from around 3500 to more than 6100 in the same period (Table 12 bottom). The male:female ratio of standardized rates has

decreased from 6.7 to 2.1 in the observation period. This ratio will further decrease to 1.5 in 2003-2007 and to 1.3 in 2018-2022. In this last period, world standardized rates for Swedish and Icelandic women are predicted to overtake the male rates for the respective country.

 

Comments

Cigarette smoking is the predominant risk factor for lung cancer (Tomatis et al., 1990), accounting for about 85% of all incident cases among men and 80% in women in the Nordic countries (Olsen et al., 1997). A much more minor risk factor is indoor radon, estimated to produce 180 cases annually in the Nordic countries after adjustment for smoking. Occupational exposures may account for as many as one fifth of cases in men (up to 1000 cases). However, smoking habits clearly drive the predicted and observed trends (Engeland et al., 1993). The prevalence of smokers in Finland halved from the early 1960s to the 1980s, in parallel with a change in types of tobacco smoked. In Denmark, the prevalence of smoking in men dropped continuously from about 80% daily smokers in the early 1950s to 30% in 2001, while among females, smoking reached a maximum of 47% in 1970, after which the prevalence decreased in parallel with that in men to reach 30% in 2001. The resulting trend in lung cancer incidence was not well estimated by Engeland et al. (1993), so that the number of cases predicted was too high. The present redictions also seem to fail to allow for the effects of recent trends in smoking prevalence, particularly among women. Nevertheless, the patterns of smoking habits tabulated by Olsen et al. (1997) explain the differences and trends in incidence that are being observed. With one third of the population still smoking in Denmark, there is clearly scope for further prevention of smoking.