Seattle – If screening availability was equalized, the U.S. Black population would have a greater colorectal cancer incidence reduction than the White population, because of its slightly higher risk, according to a new study.
“This demonstrates that observed Black–white differences in CRC incidence rates are largely driven by screening disparities rather than risk differences,” explain1Fred Hutchinson Cancer Center-lead authors, including participation from the Greater Los Angeles VA Healthcare System.
The report in the Journal of the National Cancer Institute Monographs points out that the Black population in the United States has higher colorectal cancer (CRC) incidence rates and worse CRC survival than the U.S. white population. It also has historically lower rates of CRC screening, according to the authors.
The study analyzed Surveillance, Epidemiology, and End Results(SEER) incidence rate data in patients diagnosed between the ages of 20 and 45 years, before routine CRC screening is recommended. The researchers identified a rapid rise in rectal and distal colon cancer incidence in the white population but not the Black population, and little change in proximal colon cancer incidence for both groups.
The study notes that, In 2014-2018, CRC incidence per 100 000 was 17.5 (95% confidence interval [CI] = 15.3 to 19.9) among Black people aged 40–44 years and 16.6 (95% CI = 15.6 to 17.6) among White people aged 40–44 years. A difference was that 42.3% of CRCs diagnosed in Black patients were proximal colon cancer, and 41.1% of CRCs diagnosed in white patients were rectal cancer. A
The analyses used a race-specific microsimulation model to project screening benefits, based on life-years gained and lifetime reduction in CRC incidence, assuming these Black-White differences in CRC risk and location.
Results indicate that the projected benefits of screening (via either colonoscopy or fecal immunochemical testing) were greater in the Black population, suggesting that observed Black-White differences in CRC incidence are not driven by differences in risk.
“In the United States, there are clear racial and ethnic differences in the burden of CRC, which are especially well-documented for the Black population,” according to background information in the article. “Here and throughout, reference to Black and White populations is a shorthand for populations that are segmented based on a race-attribute, a social rather than biological construct that reflects exposure to racism. CRC incidence rates are higher in the Black population than in the white population, and compared with white CRC patients, Black patients tend to be diagnosed at a younger age and have poorer stage-specific survival, with 40% higher CRC-specific mortality rates.”
The authors suggest that differences in CRC burden can arise through at least two pathways: differences in risk and differences in care (including both screening and treatment); they maintain that social determinants of health and structural racism underlie both pathways.
While screening initiation has historically been lower in Black populations than in white populations, the differences have diminished over time, according to the authors, who add that patients in the same health system, regardless of race, also have similar rates of timely follow-up after an abnormal stool-based test.
“At the same time, there is evidence of Black–white disparities in CRC treatment, consistent with CRC mortality differences,” the researchers advise. “Compared with white patients, Black patients are less likely to be treated for CRC than White patients, with lower rates of surgical resection and adjuvant chemotherapy, and are more likely to experience treatment delays.
They note that incidence of early onset CRC provides a natural experiment for understanding Black–White differences in risk because routine screening was not recommended before age 50 years until recently:
- In 2009, the American College of Gastroenterology first recommended that Black people begin screening at age 45 years.
- In 2018, the American Cancer Society lowered the age for all people to begin screening to age 45 years.
- In 2021, the US Preventive Services Task Force (USPSTF) also recommended that CRC screening begin at age 45 years.
- Rutter CM, Nascimento de Lima P, Maerzluft CE, May FP, Murphy CC. Black-White disparities in colorectal cancer outcomes: a simulation study of screening benefit. J Natl Cancer Inst Monogr. 2023 Nov 8;2023(62):196-203. doi: 10.1093/jncimonographs/lgad019. PMID: 37947338; PMCID: PMC10637026.
