1. While carcinoids contribute more heavily to the total incidence of early-onset colorectal cancer than they did in 2000, adenocarcinomas have also become more prevalent in nearly all subgroups.
2. Younger patients are experiencing the greatest growth in incidence rate, highlighting the necessity of risk-stratification and early diagnostic testing.
Evidence Rating Level: 2 (Good)
Study Rundown: Colorectal cancer is the third leading cause of cancer death in the United States, with a lifetime risk of roughly 1 in 25 in both men and women. While the overall incidence of colorectal cancer has been decreasing for the past several decades according to SEER data, detected cases of early-onset colorectal cancer (EOCRC) have instead been steadily rising in number. Previous analyses have generally focused on overall CRC incidence with little emphasis on specific histological subtypes. However, identification of the fastest-growing cancer types and the highest risk groups is critical in order to better inform the potential modification of controversial screening guidelines. This retrospective study found that, while the two youngest age groups still had the lowest absolute incidence rates, they also experienced the steepest increase in rectal adenocarcinoma. While adenocarcinoma comprised the bulk of CRC cases throughout the study, these changes were generally overshadowed by the increase in carcinoid tumors across all age groups, resulting in an increased contribution to the total number of CRC cases over time. It is unclear whether these trends can be attributed to a true increase in tumors due to lifestyle factors or simply to advances in endoscopic detection, but the results of this study reflected the importance of maximizing screening efforts in older and higher-risk individuals. Further, the finding that adenocarcinomas were found to be increasing in the most early-onset subgroups had implications for the adjustment of the average-risk screening age from 50 to 45 years.
In-Depth [retrospective cohort]: This study utilized SEER 18 data from 2000 to 2016 to examine all CRC cases in patients between the ages of 20 and 54 years. To minimize the effects of short-term fluctuations in incidence rate, rate comparisons were generated using a three-year average for the study period flanks (2000-2002 and 2014-2016). While the two younger age groups had manifold fewer cases overall compared to the two older age groups (16131 versus 107012 cases), they also had the greatest change in adenocarcinoma incidence. Specifically, there were increases of 39% in rectal-only cases in both patients aged 20-29 years (0.33 to 0.46 per 100,000) and those aged 30-39 years (1.92 to 2.66 per 100,000); colon-only cases in those aged 30-39 years also increased by 20% (3.30 to 3.97 per 100,000). Smaller increases in the range of 10-16% were also observed in the 40-49 and 50-54 age groups. The only categories that did not display a statistically significant gain in adenocarcinoma incidence over time were colon-only cases in the youngest age group and both colon-only and colorectal cases in the oldest. On the other hand, rectal carcinoid tumors increased significantly in all age groups, with the steepest changes occurring in those aged 20-29 (113% [0.08 to 0.17 per 100,000]) and those aged 50-54 (+159% [2.36 to 6.10 per 100,000]).
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