Carcinoids contributed to recent increase in early-onset colorectal cancer rates

While colorectal carcinoid rates are increasing more quickly than colorectal adenocarcinoma rates in younger patients, adenocarcinomas are steadily increasing in almost all early-onset subgroups, including those in their 40s, a U.S. study found.

In recent years, colorectal adenocarcinoma rates increased in most early-onset subgroups, and carcinoids are increasing at a faster rate, at least in part because of increased detection and case capture by cancer registries, a study found.

Researchers reviewed data from Surveillance, Epidemiology, and End Results 18 (SEER 18) from 2000 to 2016 for 119,624 patients with colorectal cancer to assess early-onset incidence rates and changes over time, stratified by histologic subtype. They reviewed incident rates per 100,000 population, changes in three-year moving averages (pooled rates from 2000 to 2002 vs. those from 2014 to 2016), and the annual percentage change among patients in their 20s, 30, and 40s, as well as those ages 50 to 55 years. Results were published online on Dec. 15 by Annals of Internal Medicine.

The steepest changes in three-year moving average incident rates for adenocarcinoma were for rectal-only cases in patients ages 20 to 29 years (increase, 39% [0.33 to 0.46 per 100,000]) and ages 30 to 39 years (increase, 39% [1.92 to 2.66 per 100,000]) and for colon-only cases in patients ages 30 to 39 years (increase, 20% [3.30 to 3.97 per 100,000]) (P<0.050 for all comparisons). Corresponding annual percentage changes were 1.6%, 2.2%, and 1.2%, respectively (P<0.050 for all comparisons). For patients in their 40s, three-year moving average incident rates increased in both colon-only (increase, 13% [12.21 to 13.85 per 100,000]) and rectal-only subsites (increase, 16% [7.50 to 8.72 per 100,000]) (P<0.050 for both comparisons).

Carcinoid tumors were common, representing approximately 4% to 20% of all colorectal cancer cases and 8% to 34% of all rectal cancer cases, depending on age group and calendar year. Colon-only carcinoid tumors were rare. Colorectal carcinoid tumor incident rates increased more steeply than those for adenocarcinoma in all age groups, which affected the contribution of carcinoid tumors to overall cancer cases over time. These changes were driven by rectal subsites and were most pronounced in patients ages 50 to 54 years, in whom rectal carcinoid tumors increased by 159% (2.36 to 6.10 per 100,000) between 2000 to 2002 and 2014 to 2016, compared with 10% for adenocarcinoma (18.07 to 19.84 per 100,000), ultimately accounting for 22.6% of all rectal cancer cases.

According to the researchers, the findings show the importance of assessing histologic subtypes independently. If all colorectal cancers are grouped together without stratifying by histologic subtype, it may not be possible to get an accurate account of adenocarcinomas in young patients, they said. Given the focus on early-onset colorectal cancer, it is critical to focus specifically on adenocarcinomas, the researchers noted.

While carcinoids are increasing at a faster rate than adenocarcinomas, adenocarcinomas are steadily increasing in almost all early-onset subgroups, including patients in their 40s. This has implications for changing average-risk screening to age 45 years, the authors said, noting that adenocarcinomas still make up the overwhelming majority of colorectal cancer cases in younger patients. For those in their 20s and 30s, the increasing adenocarcinoma rates underscore the importance of risk-stratifying patients by family history and taking such symptoms as rectal bleeding seriously, they said.

The medical community, patient organizations, and policymakers have all been concerned about a worrisome increase in colorectal cancer in young adults in recent years, an editorial noted. This new study is important because it shows that carcinoids contribute to some of the previously reported increase in cancer, the authors said.

“With the data reported in Annals and the inherent uncertainty of guidelines based on modeling, caution is warranted when promoting the benefits of CRC [colorectal cancer] screening for persons younger than 50 years,” they wrote. “Scientific equipoise regarding the efficacy of CRC screening in young adults still exists. Equipoise situations in modern medicine call for clinical trials, not broad recommendations for implementation.”