Colonoscopy Screen Shows More Advanced Cancers in White Men

Fran Lowry

July 03, 2013

White men are more likely than black men to have advanced colorectal neoplasia (ACN) at screening colonoscopy in a safety net hospital, according to a new study published in the July 2 issue of the Annals of Internal Medicine.

"Black persons are more likely than white persons to be diagnosed with colorectal cancer and to die from it," write Paul C. Schroy III, MD, MPH, from Boston University School of Medicine, Massachusetts, and colleagues. "The extent to which genetic or biological factors versus disparities in screening rates explain this variance remains controversial."

To shed some light on the controversy, the authors aimed to compare the prevalence and distribution of ACN among average-risk white and black persons undergoing screening colonoscopy in a safety net hospital while controlling for other epidemiologic risk factors.

The researchers conducted a cross-sectional survey of consecutive, asymptomatic, average-risk patients who had screening colonoscopy between March 2005 and January 2012 at Boston Medical Center, a private, not-for-profit, community-based academic medical center.

The center is the largest safety net hospital in New England and has a legislative mandate to provide care to low-income persons and other vulnerable populations regardless of their ability to pay, the authors note.

The study subjects were aged 50 to 79 years, (mean age, 56 years) and self-categorized as non-Hispanic white (n = 1172) or non-Hispanic black (n = 1681). None had symptoms that might indicate colorectal cancer or had a family history of colorectal cancer.

An advanced colorectal neoplasm was defined as a tubular adenoma 10 mm or more in size, an adenoma of any size with villous features or high-grade dysplasia, a dysplastic serrated lesion of any size, or invasive cancer.

The researchers found that the unadjusted prevalence of ACN was significantly higher among white patients than black patients (6.8% vs 5.0%; P = .039). The difference was more pronounced in men, with 9.3% of white vs 5.7% of black men being diagnosed with ACN.

After adjusting for a variety of factors, including sociodemographic and risk factors including body mass index, smoking, alcohol intake, aspirin and nonsteroidal anti-inflammatory drug use, red meat consumption, calcium and vitamin D intake, use of oral contraceptives or hormone replacement therapy, physical activity, and diabetes mellitus, black men were still less likely than white men to have ACN (adjusted odds ratio [AOR], 0.59; 95% confidence interval [CI], 0.39 - 0.89) at the time of screening colonoscopy.

No statistically significant difference was seen for women (AOR, 1.32; 95% CI, 0.73 - 2.40).

After adjusting for age and sex, black patients with ACN had a higher percentage of proximal disease (52% vs 39%) than white patients (P = .055).

"Our study affirms the importance of race as an independent risk factor," the authors write. "However, contrary to the results of several previously published studies, we found that the prevalence of ACN was higher among white persons than black persons overall, especially white men compared with black men after adjustment for other known [colorectal cancer] risk factors"

They point out that their study has "several noteworthy strengths that lend credence to our findings."

Among these strengths are the prospective enrolment of patients, which allowed the researchers to control for previous colonoscopy and other epidemiologic risk factors, thereby minimizing confounding; the safety net healthcare setting, which enabled assessing the prevalence of ACN in a population that often has financial barriers to colorectal cancer screening; and the fact that the researchers used a more valid measure of ACN than polyp size alone.

Limitations of the study include that it was done at a single, urban, academic medical center, the use of a convenience sample, and the lack of sufficient statistical power for many subgroup analyses, particularly women, because of the relatively low prevalence of disease. In addition, data on race and ethnicity were self-reported, and persons younger than 50 years were not included.

Despite these limitations, the authors write that their findings "have important public health implications because they highlight the need for strategies focusing on increasing screening rates among black persons in settings where disparities exist."

"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," the researchers conclude. "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."

The study was supported by the National Cancer Institute. The authors have disclosed no relevant financial relationships.

Ann Intern Med. 2013;159:13-20. Abstract

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