The incidence of colorectal cancer (CRC) began to increase in adults aged <50 years from 1981 to 1985, indicating that the increase may be attributed to risk factors such as obesity, researchers reported in Gastroenterology.
The investigators assessed CRC incidence rates from 1935 to 2017 using the Connecticut Tumor Registry, a population-based registry of all cancers diagnosed in Connecticut residents since 1935. This registry includes nearly 4 more decades of data than national cancer registries.
The study authors evaluated CRC incidence trends stratified by sex and age group, including participants aged 25 to 49 (and 25 to 39), 50 to 69, and 70 to 84 years.
CRC incidence significantly increased among women aged 25 to 49 years at an annual percent change (APC) of 1.75% (95% CI, 1.18-2.32) from 1985 to 2017. This increase had been preceded by a decreasing incidence from 1953 to 1985. In men aged 25 to 49 years, CRC incidence was stable between 1935 and 1974, and decreased from 1974 to 1981 (although the APC was not statistically significantly different from zero). CRC incidence in men also significantly increased from 1981 to 2017 (APC, 1.99%; 95% CI, 1.55-2.43). Similar trends were observed when the evaluation included only participants aged 25 to 39 years.
After the findings were stratified by subtype, the incidence of rectal cancer, but not distal or proximal colon cancer, significantly increased in recent decades in women and men aged 25 to 49 years. In adults aged ≥50 years, CRC incidence rates significantly decreased across most time points from 1985 to 2017.
The researchers noted several study limitations, as their findings are based on cancer registry data strictly from the Connecticut Tumor Registry, restricting its generalizability. Additionally, early trends could have been influenced by changes in data quality over time. Finally, stage-specific incidence trends were not assessed due to missing data in early years.
“[T]his study offers strong support that early-onset CRC did not begin to significantly increase in women or men until the 1980s,” the investigators commented. “Future studies should thus consider cohort-specific trends in CRC incidence and exposures that have changed in recent birth cohorts. This includes obesity-related risk factors, given that our findings support that early-onset CRC incidence was not increasing for several decades prior to the rise in obesity in the U.S.”
Kehm RD, Lima SM, Swett K, et al. Age-specific trends in colorectal cancer incidence for women and men, 1935-2017. Gastroenterol. Published online May 28, 2021. doi:10.1053/j.gastro.2021.05.050