The Incidence of Colorectal Cancer Is Decreasing in the Older Age Cohorts in the Zaanstreek Region in the Netherlands: An Age-Cohort Effect

Introduction. Colorectal cancer (CRC) has a high incidence. Removal of adenomas, the precursor lesion, could be helpful in the prevention of cancer. Aim. To investigate the yearly incidence of CRC in consecutive years. Patients and Methods. All patients diagnosed with CRC in the years 1990 till 2010 were studied. Date of diagnosis, age at time of diagnosis, gender, and localisation of the tumour were assessed. Results. A total of 1575 incident CRC were diagnosed, 865 men (55%) and 710 women (45%). CRC occurred more often in men. In the course of the years, the occurrence of CRC increased. After exclusion of rectal cancer, the percentage of proximal cancer in the colon shows a trend towards increase in the consecutive years. In the twenty consecutive years, the population of the Zaanstreek region increased from 130.000 to 145.330. There was a significant increase of CRC in the age cohort 51–70 in the period of twenty years, while a significant decreasing incidence of cancer was seen in patients above 71 years. Conclusion. The decreasing incidence of colorectal cancer in the age cohorts above 71 years possibly reflects indirect evidence of an age-cohort effect due to removal of adenomas in these age cohorts earlier in life. 1. Introduction Colorectal cancer is a disease with a high prevalence, at least in the Western world. It is the third most diagnosed cancer and the second leading cause of death. Several studies clearly show a rising incidence, mostly explained by aging of the population [1, 2]. Evidence in the literature demonstrated that regular screening for colorectal cancer is effective in reducing incidence and mortality [3, 4]. However, screening is not yet widely available. Colorectal cancer has a well-defined precursor, namely, the adenoma. Removal of adenomas could be helpful in the prevention of cancer. Since adenomas mostly need several years to develop into cancer, and since these lesions tend to occur at younger age, screening for adenomas is recommended above the age of 50 years. Since more than 20 years adenomas are removed presumably endoscopically, it could be expected that the incidence of colorectal cancer should be decreasing. In this time period most patients underwent colonoscopy because of clinical complaints, and adenomas could be detected not only as the cause of, for instance, bleeding but also as innocent bystander not responsible for any complaint. Statistics do not show a decrease in colorectal cancer incidence. A major problem with population based statistics is that these only report on total numbers in the population