| Summary: | Background The incidence of colorectal cancer in patients aged less than 50 years is increasing in Western countries. This population‐based study investigated the age‐ and sex‐specific incidence of colorectal cancer over time in Sweden, and characterized trends in tumour localization and stage at diagnosis. Methods Patients diagnosed with colorectal cancer between 1970 and 2016 were identified from the Swedish Cancer Registry, and categorized by sex, age and tumour location. The incidence and average annual percentage change (AAPC) were estimated and compared between age groups. Results There was an overall increase in the incidence of colorectal cancer between 1970 and 2006, but a decrease in 2006–2016 (AAPC −0·55 (95 per cent c.i. −1·02 to −0·07) per cent). The largest increase in colonic cancer was in 1995–2005 in women aged less than 50 years (AAPC 2·30 (0·09 to 4·56) per cent versus 0·04 (−1·35 to 1·44) and − 0·67 (−1·62 to 0·28) per cent in women aged 50–74 and 75 years or more respectively). Since 1990, rectal cancer increased in patients of both sexes aged below 50 years, with higher AAPC values in women (2006–2016: 2·01 (−1·46 to 5·61) per cent versus 0·20 (−2·25 to 2·71) per cent in men). Younger patients were more likely than those aged 50–74 and 75 years or more to present with stage III–IV colonic (66·2, 57·6 and 49·6 per cent respectively) and rectal (61·2, 54·3 and 51·3 per cent) cancer. From the mid 1990s, rates of proximal and distal colorectal cancer, and rectal cancer were increased in patients aged less than 50 years. Conclusion The overall incidence of colorectal cancer in Sweden decreased in the past decade. However, in patients under 50 years of age the incidence of colorectal cancer – proximal, distal and rectal – continued to increase over time.
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