Increase of early-onset colorectal cancer: a cohort effect.

Increasing incidence rates of early-onset colorectal cancer (ie, <50 years of age) have been reported across multiple countries. We investigated long-term cancer incidence data from 1995 or earlier from Australia, Canada, England, and the United States separately by sex. Estimated annual percentage change and age-period-cohort models were used to assess trends by country and sex. All countries showed increasing early-onset colorectal cancer incidence in successive birth cohorts since 1960, with individuals born in the 1990s facing at least 4-fold higher risks than individuals born in the 1960s. Cohort effects were observed across all countries, with sharper increases at younger ages. Over the most recent decade, the estimated annual percentage change ranged from 3.4% in Australia and the United States to 4.5% in England, with steep rises before age 40 years. The emergence of these trends from ages 20 to 29 years suggests that contributing factors may originate early in life and reflect exposures whose effect begin in youth and accumulate throughout the lifespan.