Colorectal cancer (CRC) is the second leading cause of death from cancer in both men and women in the U.S. Thanks in large part to increased screening of those over age 50 in last decade, overall CRC rates have been falling among the general population.
However, the incidence of CRC among younger individuals in the U.S. is rising at an alarming rate. Over the past 20 years, the rate of CRC has increased by 2.2% per year in people under age 50.
Hidden within these statistics are the significant disparities in CRC incidence and outcomes that exist for African Americans.
Compared to whites, African Americans have a 20% higher incidence of CRC. They are more likely to develop CRC at younger ages, be diagnosed further along in their illness, and are more likely to die of their disease. African Americans have the lowest five-year survival rate for CRC of any racial group in the U.S.
Absolute rates of early-onset CRC, generally defined as CRC diagnosed before age 50 to 55, are higher among African Americans compared to whites. The recent deaths of Chadwick Boseman at age 43 and Natalie Desselle-Reid at age of 53 serve as tragic examples of the disproportionate impact of early-onset CRC among the African American community.
Many factors may increase early-onset CRC risk
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The reasons for this racial disparity in early-onset CRC are unclear. This is not surprising, given our overall lack of understanding of the factors driving the increased incidence of early-onset CRC across all races.
Some factors that have been linked with early-onset CRC include obesity, physical inactivity and unhealthy dietary patterns. According to data from a National Institutes of Health/AARP survey, each of these risk factors may be more prevalent in African American communities, particularly those of low socioeconomic status.
African Americans are also less likely to have access to health care. As a result, they may not be able to promptly seek medical care for symptoms associated with colorectal polyps or cancer. This, in turn, could delay detection of tumors, which could be cured by removal through colonoscopy or surgery if detected early enough.
Finally, for reasons that are not entirely clear, once diagnosed, African Americans are less likely to receive chemotherapy or surgery compared to white patients.
Underlying these potential explanations are pervasive inequities based on socioeconomic status and systemic racism.
Biological features associated with disparities
African Americans are also more likely to be diagnosed with a CRC that originated in the right colon, rather than in the left colon or the rectum. As I noted in an earlier blog post, right-side colon cancers may be more difficult to detect, and they have a worse prognosis compared with left-side CRCs.
Recent studies suggest that differences in the epigenome of the right colon relative to the left colon among African Americans, compared with the pattern seen among whites, could explain racial differences in the site at which CRCs originate. (An epigenome consists of chemical compounds that attach to a person’s DNA and influence its expression.) Some data suggest that there may be variation in the molecular profile of tumors that develop in African Americans compared to whites, which may indicate that the pathways that initiate or encourage progression of cancers may differ by race. Differences in the gut microbiome have been increasingly implicated in the rising incidence of early-onset CRC, and may also contribute to higher CRC incidence in African Americans.
Screening guidelines may leave Blacks behind
Until recently, most expert bodies have not generally recommended CRC screening of average-risk individuals younger than age 50, with only the American College of Gastroenterology and American Society for Gastrointestinal Endoscopy recommending earlier screening among African Americans. However, in 2018 the American Cancer Society (ACS) modified their guidelines to recommend beginning screening at age 45 for individuals of all races. And in May 2021, the U.S. Preventive Services Task Force revised its advice regarding screening for colorectal cancer, lowering the recommended age for first screening from 50 to 45.
These newer guidelines are expected to have an impact in reducing early-onset CRC incidence. However, significant concerns remain about persistent disparities between African Americans and whites in access to, and participation in, CRC screening. Furthermore, rates of early-onset CRC have risen sharply among individuals between the ages of 20 and 45; the revised guidelines will not apply to most people in this age group.
Given the increasing attention on early-onset CRC, and the longstanding problem of racial disparities in CRC incidence and outcomes, there will hopefully be significant progress in the coming years in addressing these converging public health priorities. This should include continued research into the causes of early-onset CRC, improving early detection through screening and prevention, and ensuring access to effective treatment. However, because the root cause of many CRC disparities lies in socioeconomic and racial inequities, there remains a high unmet need for the medical and public health communities to address these broader issues.
(Andrew Chan, M.D., MPH, is a contributor to Harvard Health Publications.)