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Advanced colorectal neoplasia more likely in white men
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White men were significantly more likely to have advanced colorectal neoplasia at screening than black men, according to results of a cross-sectional survey.
The findings contradict those of several previously published studies that suggested risk was higher among blacks, who are more likely to be diagnosed with colorectal cancer and die from it.
Paul C. Schroy III
Paul C. Schroy III, MD, MPH, a professor of medicine and epidemiology at Boston University School of Medicine, and colleagues conducted the study from March 2005 to January 2012 at Boston Medical Center, an open-access, academic, safety-net hospital.
The prevalence and location of advanced colorectal neoplasia — defined as tubular adenoma ≥10 mm, any adenoma with villous features, invasive cancer or a dysplastic serrated lesion of any size — served as the primary endpoint.
The analysis included 2,853 asymptomatic, average-risk adults aged 50 to 79 years who were undergoing screening colonoscopy. Of them, 1,681 were white and 1,172 were black.
Participants completed a questionnaire that covered all 21 items on the Your Disease Risk assessment tool for colorectal cancer, as well as questions related to several other factors, such as race and ethnicity; age, height and weight; dietary intake; previous screening habits; smoking history; history of aspirin or NSAID use; family history of colorectal polyps; and diabetes history.
Results indicated prevalence of advanced colorectal neoplasia was higher among white patients than black patients (6.8% vs. 5%; P=.039). However, prevalence varied by sex. Among men, prevalence was higher among whites (9.3% vs. 5.7%), whereas among women, prevalence was higher among blacks (4.3% vs. 3.5%; interaction P=.034).
After researchers controlled for other epidemiologic risk factors, results indicated black men were 41% less likely than white men to have advanced colorectal neoplasia (adjusted OR=0.59; 95% CI, 0.39-0.89). Researchers reported no significant difference for women (aOR=1.32; 95% CI, 0.73-2.40).
The results also indicated black patients with advanced colorectal neoplasia had a higher percentage of proximal disease after adjustments for sex and age (52% vs. 39%; P=.055).
Researchers indicated the study was limited by its single-institution design, as well as its inadequate statistical power for recall bias and subgroup analyses.
“Our findings provide new evidence suggesting that disparities in access to screening and differential exposure to modifiable risk factors rather than genetic differences are largely responsible for the higher overall incidence of colorectal cancer among black persons, especially men,” Schroy and colleagues wrote. “Future studies are warranted to better define the extent to which genetic or biological factors might explain the predilection for proximal disease among black persons.”
Disclosure: The researchers report grant support from NCI.
Perspective
Back to TopAlexandria T. Phan, MD
In a single-center, 7-year cross-sectional analysis of 2,853 asymptomatic patients with average risk for colorectal cancer undergoing screening colonoscopy, Schroy and colleagues showed that the prevalence of advanced colorectal neoplasia (ACN) was higher in white men than black men.
Among the patients with ACN, blacks were more likely than whites to have proximal disease in the transverse colon, hepatic flexure, ascending colon or cecum (52% vs. 39%), although the difference fell shy of statistical significance after adjustment for age and sex (P=.055). This observation is perhaps the most interesting finding of the study. Although it may not be unique, it adds support to the concept that the heterogeneity of colorectal cancer derives from their molecular and genetic difference.
Microsatellite instability (MSI) represents a distinct form of genomic instability. The CpG island methylation phenotype (CIMP) is a distinct form of epigenomic instability, which causes most sporadic MSI-high colorectal cancers through epigenetic inactivation of MLH1 (Nosho K. PLoS One. 2008;doi:10.1371/journal.pone.0003698). Independent of MSI, CIMP-high colorectal cancer is associated with proximal tumor location, old age of onset, female sex and the BRAF mutation (Samowitz WS. Gastroenterology. 2005;129:837-845).
Accumulating evidence suggests that proximal colon cancer and distal colon cancer differ in various molecular features, including CIMP and MSI. Colorectal cancers encompass a heterogeneous group of diseases with complex genetic and epigenetic alterations. Molecular classification is thus increasingly important for clinical decision making.
The study had several limitations, including the use of patients from a single center, retrospective and selection biases, insufficient statistical power for many of the subgroup analyses, and potential for misclassification of race. Because of these important limitations, the analysis is underpowered to draw any conclusive practice-changing recommendations. The incidence and mortality of colorectal cancer in the United States are consistently highest among black Americans. Still controversial is the extent to which disparities in colorectal screening rates or genetic differences contribute to ethnic variance.
In fact, better understanding of the molecular differences of colorectal cancer will likely generate the explanation to the disparity of colorectal cancer outcomes among different ethnic populations. Therefore, research efforts and national policy should continue to address both social and biological factors in the ethnic disparity of colorectal incidence and mortality.
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