Steepest changes in adenocarcinomas in younger groups
In their study, Dr. Karlitz and colleagues assessed the incidence rates of early colorectal cancer, using SEER data from 2000 to 2016, and stratifying the data by histologic subtype (primarily adenocarcinoma and carcinoid tumors), age group (20-29, 30-39, 40-49, and 50-54 years), and subsite.
A total of 123,143 CRC cases were identified in 119,624 patients between the ages of 20-54 years during that time period.
The absolute incidence rates in the younger age groups (20-29 and 30-39 years) were very low, compared with those aged 40-49 and 50-54 years.
The greatest 3-year average annual incident rate changes in adenocarcinoma (2000-2002 vs. 2014-2016) for any age group or subsite were for rectal-only cases in the 20-29 years group (+39%), as well as rectal-only cases in those aged 30-39 years (+39%), and colon-only cases in the age 30-39 group (+20%).
There was also significant increase in rectal-only adenocarcinoma in individuals aged 50-54 years (+10%). A statistically significant increase in the annual percentage change for adenocarcinomas was observed for all age groups, except for colon-only cases in the 20-29 years group (0.7%) and for both colorectal (0.2%) and colon-only cases (–0.1%) in those aged 50-54 years.
Even though the absolute carcinoid tumor incidence rates were lower than for adenocarcinoma in all age groups and subsites, a statistically significant increase was observed in the 3-year average annual incidence rate of combined-site colorectal carcinoid tumors in all age groups from 2000–2002 and 2014–2016. This increase was largely the result of increases in rectal carcinoid tumors, the authors note.
The authors also highlighted the results in the 40- to 49-year age group “because of differing opinions on whether to begin average-risk screening at age 45 or 50 years.”
They reported that rates of rectal and colon adenocarcinoma are increasing “substantially,” whether measured by changes in 3-year average annual incidence rate or by annual percentage changes. The change in average annual incidence rate of colon-only adenocarcinoma for persons aged 40-49 years was 13% (12.21 to 13.85 per 100,000), and that of rectal adenocarcinoma was 16% (7.50 to 8.72 per 100,000). Corresponding annual percentage changes were 0.8% and 1.2%, respectively. “These significant increases in adenocarcinoma incident rates add to the debate over earlier screening at age 45 years,” they commented.
Calls for next steps
The editorialists emphasize restraint when promoting the benefits of colorectal screening for persons younger than 50 years.
They point out that the USPSTF released a provisional update of its CRC screening recommendations about lowering the age to initiate screening to 45 years, as reported by this news organization.
“No new empirical evidence has been found since the USPSTF update in 2016 to inform the effectiveness of screening in persons younger than 50 years,” they write, adding that similar to the American Cancer Society in 2018, the task force has relied exclusively on modeling studies.
This new data from Dr. Karlitz and colleagues “should prompt the modelers to recalculate their estimates of benefits and harms of screening,” they suggested. “Revisiting the model would also allow competing forms of CRC screening to be compared in light of new risk assumptions.
“Previous assumptions that screening tests are equally effective in younger and older patients and that screening adherence will approach 100% may also be reconsidered,” the editorialist commented.
The study authors concluded somewhat differently.
“In conclusion, adenocarcinoma rates increased in many early-onset subgroups but showed no significant increase in others, including colon-only cases in persons aged 20-29 and 50-54 years,” the investigators wrote.
They also observed that “rectal carcinoid tumors are increasing in young patients and may have a substantial impact on overall CRC incident rates.”
Those findings on rectal carcinoid tumors “underscore the importance of assessing histologic CRC subtypes independently,” the researchers said.
This new approach, of which the current study is a first effort, “may lead to a better understanding of the drivers of temporal changes in overall CRC incidence and a more accurate measurement of the outcomes of adenocarcinoma risk reduction efforts, and can guide future research.”
The study had no outside funding. Dr. Karlitz reported personal fees from Exact Sciences, personal fees from Myriad Genetics, and other fees from Gastro Girl and GI OnDEMAND, outside the submitted work. Dr. Bretthauer reports grants from Norwegian Research Council, grants from Norwegian Cancer Society for research in colorectal cancer screening. Dr. Weinberg and Dr. Kalager have disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.