Incidence rates of early-onset colorectal cancer (CRC) are similar among Black and White individuals aged 40 to 49 years, though cases have increased over time among White adults, according to an analysis of data from the Surveillance, Epidemiology, and End Results (SEER) 18 database. The authors noted that trends in incidence rates over time may be related to the adoption of CRC screening guidelines.
Additionally, the researchers noted a reduced incidence of rectal cancer in Black individuals compared with White counterparts, as well as increasing differences in rates of rectal cancer between Black and White women.
This study was published in JAMA Network Open.
Colorectal Cancer Screening Guidelines
Guidelines for screening for CRC in people aged under 50 years have changed over time. The American College of Gastroenterology (ACG) recommended in 2008 that Black individuals at average risk of CRC begin screening starting at age 45. Then in 2018, the American Cancer Society recommended that all average-risk adults begin screening at age 45, regardless of race. This screening recommendation was formally adopted by the US Preventive Services Task Force earlier this year.
“Even with the threshold finalized at age 45 years, screening rates in younger patients are markedly suboptimal (historically 28%-47% in individuals aged 50 to 54 years),” wrote the study authors. “Hence, a better understanding of the CRC burden in younger patients is required as similar issues with low screening rates, which can impede cancer prevention efforts, may be present when expanding screening to individuals aged 45 years.”
Additionally, they noted, “Race-stratified incidence rate (IR) data of those in their 40s can also assess for changes in IRs between Black and White populations that may have arisen from differential average-risk screening recommendations since the 2008 ACG guideline.”
Incidence of CRC in Patients Aged <50 Years
For this study, the researcher used the larger SEER 18 database, which features expanded race data compared with earlier SEER versions, to further analyze the burden of early-onset CRC in patients approaching screening age in the United States. Specifically, this study focused on incidence according to adenocarcinoma histologic subtype.
“Early-onset colorectal cancer incidence rates are rising faster in White individuals than Black individuals,” wrote the study authors. “However, prior National Cancer Institute SEER racial stratification analyses used smaller SEER 13 databases, combined patients under age 50 years, did not stratify by sex, and did not focus on adenocarcinoma histologic subtypes (screening target).”
The SEER 18 database includes information on cases from 2000 through the present. The researchers identified annual age-adjusted CRC incidence rates through 2017 among individuals aged 40 to 49 years. These data were stratified by anatomic subsite (colon or rectum), adenocarcinoma histology, race (non-Hispanic Black or non-Hispanic White), and sex. The investigators calculated the yearly annual percent change (APC) incidence rates and between-group annual rate ratios (ARRs).
The total cohort included 46,728 colorectal cancer cases (n = 45,429 patients). Of this population, 6,480 patients (14.2%) were Black and 27,426 (60.4%) were White. The mean age was 45.5 years.
Rates of Early-Onset CRC by Subtype
Overall, the researchers reported no significant difference in ARRs of absolute incidence of early-onset colorectal cancer between White and Black individuals between 2014 and 2017. The rate of colorectal adenocarcinoma has increased over time among White patients, from 19.6 cases per 100,000 person-years (PY) in 2000 to 25.2 per 100,000 PY in 2017 (APC = 1.6, 95% confidence interval 1.3-1.9). In contrast, incidence rates were not significantly changes for Black patients during this time (2000, 26.4/100,000 PY; 2017, 25.8/100,000 PY; APC = -0.03, 95% CI -0.5-0.5). There was a 4.1% increase in rates of CRC in Black patients from 2008 to 2010 (15.1 to 21.3 per 100,000 PY), which the authors commented was coincident with the 2008 ACG guidelines.
The researchers noted that the absolute incidence rates of colonic adenocarcinoma remain higher in Black patients compared with White patients.
“Although absolute colon adenocarcinoma IRs in Black individuals are higher than in White individuals, colon adenocarcinoma APCs in Black individuals have remained stable in comparison with White individuals in whom IRs are increasing,” they noted.
Regarding rectal-only adenocarcinoma, incidence rates were similar between White and Black patients through 2008; however, as of 2009, incidence has significantly diverged, the authors noted. By 2017, the absolute incidence rates of rectal cancer were 39% higher in White compared with Black individuals, with increasing APC (APC = 2.2; 95% CI 1.6-2.8). Rates of rectal cancer were decreasing among Black individuals by 2017, but this figure was not statistically significant (APC = -1.4; 95% CI -2.6-0.1). The largest divergence in APCs between study sugroups was in the risk of rectal adenocarcinoma between White women (APC =2.2, 95% CI,1.6-2.8) and Black women (APC = -1.7, 95% CI -3.6-0.3)
Impact of Screening Guidelines on Cancer Rates
In summary, the authors wrote, “This study found that colorectal adenocarcinoma incidence rates in people aged 40 to 49 years were increasing among White individuals but stabilized among Black individuals with absolute incidence rates becoming equivalent.”
The authors argue that the introduction of the screening threshold in Black adults is a possible contributor to these trends. “Rectal adenocarcinomas in Black individuals became significantly lower compared with White individuals starting in 2009. There was also a steep 41.1% increase in colon cancer rates from 2008 to 2010 in Black individuals … This finding could be consistent with initial detection of preclinical colonic lesions owing to screening initiation. Stabilization in colon adenocarcinoma rates and decreases in rectal adenocarcinoma rates thereafter would be ultimately consistent with cancer prevention.”
