The researchers assessed early-onset CRC incident rates and changes in incident rates over time, stratified by histologic subtype (primarily adenocarcinoma and carcinoid tumors), using SEER data from 2000 to 2016 for 119,624 patients with CRC.
"This is the first study to analyze early-onset colorectal cancer by specific histologic subtype," Dr. Jordan Karlitz, from Tulane University, New Orleans, told Reuters Health by email.
They found that 4% to 20% of CRCs were carcincoid tumors, which are typically indolent with a better prognosis, as opposed to adenocarcinoma, the CRC subtype that is the primary focus of screening.
Incidence rates of carcinoid tumors "increased at a steeper pace than those of adenocarcinoma in all age groups, thus accounting for an increasing proportion of overall histologic subtypes over time. These changes were driven by rectal carcinoid tumors and were most pronounced in persons aged 50 to 54 years," the researchers note in their Annals of Internal Medicine paper.
"Because adenocarcinomas make up the overwhelming majority of colorectal cancers in young patients they are the main driving force behind the increased colorectal cancer burden we are seeing in young patients," Dr. Karlitz told Reuters Health.
"Additional studies are needed to better understand the rise in carcinoid tumor incidence in young patients; whether it is the result of greater detection or a true escalation in incidence due to increasing risk factors needs to be elucidated," the researchers note in their paper.
Their observations, they add, underscore the importance of assessing histologic CRC subtypes independently.
"Critically," Dr. Karlitz told Reuters Health, "we need to know if our future interventions to prevent adenocarcinomas are working and to do this we need to assure we are measuring and monitoring this specific adenocarcinoma histologic subtype and separating it out from carcinoids which are on the rise."
He added, "We firmly believe that colorectal cancer screening for average-risk patients should begin at age 45. Our study revealed steadily increasing adenocarcinomas rates in young patients, including those in their 40's. Furthermore, there are a number of other studies that support screening at age 45 as well."
In an editorial, Dr. Michael Bretthauer with the Institute of Health and Society, University of Oslo, Norway and co-authors say this analysis stratified by histologic subtype paints a "more accurate" picture of epidemiologic trends of early-onset CRC and is "important" in showing that carcinoid tumors contribute to some of the previously reported increase in CRC in young patients.
SOURCE: https://bit.ly/3r4iG3B and https://bit.ly/2LCSJHZ Annals of Internal Medicine, online December 14, 2020.
By Megan Brooks
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