Black and White Differences in Colorectal Cancer Screening and Screening Outcomes: A Narrative Review

Racial disparities in colorectal cancer incidence and mortality are well known and widely documented. Relative to non-Hispanic whites (“whites”), non-Hispanic blacks (“blacks”) tend to have higher rates of colorectal cancer incidence (1), earlier age at diagnosis (2–4), later stage at diagnosis (5), and worse stage-specific colorectal cancer mortality (6–9). These disparities have resulted in calls for earlier initiation of colorectal cancer screening for black patients (10, 11), especially black men (12).

Colorectal cancer screening first became available in 1967 (13). In the late 1980s and early 1990s, randomized trials demonstrated the effectiveness of screening to reduce mortality (14–16), leading to colorectal cancer screening guidelines in 1995 (17, 18). Currently available colorectal cancer screening tests include stool tests [guaiac-based fecal occult blood tests (FOBT), fecal immunochemical tests (FIT), and stool DNA tests], flexible sigmoidoscopy, colonoscopy, and CT colonography. Colonoscopy is both a screening test and a diagnostic test used to evaluate symptoms and follow-up abnormal results from other tests. Screening colonoscopy has been shown to reduce both incidence and mortality, with incidence reductions due to primary prevention via the removal of adenomas (19). As recently as 2008, all average-risk individuals were recommended to begin screening at age 50 (20, 21). In 2009, the American College of Gastroenterology recommended that average-risk African Americans begin screening at age 45 (22), citing the “high incidence and early onset of colorectal cancer in African Americans” (10). The Institute for Clinical Systems Improvement made a similar recommendation in 2010 (23). In 2012, the American College of Physicians recommended that African Americans begin screening at age 40 (23). In 2017, the U.S. Multi-Society Task Force on Colorectal Cancer suggested that African Americans begin screening at age 45, but noted that the evidence to support this recommendation was of low quality (24). In 2018, the American Cancer Society issued a qualified recommendation that all individuals begin screening at age 45 (25).

Before 1985, blacks and whites had similar overall colorectal cancer incidence rates and similar age-specific colorectal cancer incidence. Figure 1 shows overall colorectal cancer incidence rates for blacks and whites based on Surveillance, Epidemiology, and End Results (SEER) Program Data (estimation details are provided in the Appendix; refs. 26, 27). In 1985, President Ronald Reagan's diagnosis with colorectal cancer raised awareness about colorectal cancer (28). After 1985, colorectal cancer incidence began to decline, especially in whites. The reasons for this decline are uncertain, but may be attributed to both changes in modifiable risk factors and increased screening (29). Figure 2, which is similar to an analyses of SEER data by Murphy and colleagues (30), shows that from 1980 to 1984 blacks and whites had similar age-specific colorectal cancer incidence rates, but in 2013–2017, black/white age-specific colorectal cancer incidence begins to diverge around age 50, the recommended age to initiate colorectal cancer screening.

Two mechanisms could explain racial disparities in colorectal cancer incidence. Disparities could be attributable to differences in colorectal cancer screening utilization (6, 31, 32), or differences in risk (33, 34). Because most colorectal cancer arises through the adenoma–carcinoma pathway (35), we use adenoma prevalence as a proxy for colorectal cancer risk but do not examine mechanisms underlying risk differences. Differences in risk could be driven by racial differences in modifiable risk factors such as diet, smoking, exercise, and obesity (36), by genetic differences (10, 33), or by the interplay between modifiable and genetic risk factors. In this article, we review the literature for evidence of these two mechanisms.

We searched the PubMed and Web of Science databases to identify articles focused on differential risk of colorectal cancer by race and ethnicity or utilization of colorectal cancer screening (details, including search terms, are provided in the Appendix). We also searched for citations to two articles focused on racial differences in risk (37, 38). Our search identified 2,085 articles. This review includes information from 17 articles that reported screening outcomes (16 articles) or behaviors (14 articles) separately for both black and white U.S. study participants and included at least 100 participants of either black or white race. Screening outcomes included adenoma prevalence, screen-detected colorectal cancer rates, interval colorectal cancer rates, and screening behaviors (percent up-to-date with guidelines, percent who received a test, and percent who return for repeat testing). We excluded studies reporting only polyp prevalence, rather than adenoma prevalence, as polyps include lesions that may not harbor malignant potential.

Colorectal cancer screening includes multiple steps: initiation of screening, receipt of a follow-up colonoscopy after an abnormal referral test (e.g., after an abnormal stool-based test or flexible sigmoidoscopy), repeat screening after a normal test, and colonoscopy surveillance after adenoma detection.

Table 1 compares screening rates of black and white participants at different steps in the screening process. In addition to observed percentages, Table 1 includes unadjusted ORs and relative risks (RR), and adjusted ORs (aOR) and adjusted RRs (aRR). Each study adjusted for somewhat different factors. When multiple adjusted estimates were provided, we focused on estimates that adjusted for factors common across studies: age, sex, income, and education.

Most studies examined whether individuals were up-to-date with colorectal cancer screening guidelines in place for average-risk individuals at the time of the study, generally defined as having a FOBT or FIT in the last 1 to 3 years, receipt of flexible sigmoidoscopy in the last 5 years, or colonoscopy in the last 10 years.

There is evidence that for many years, blacks were less likely than whites to be up-to-date with colorectal cancer screening guidelines, and that these differences may be narrowing. In 1987, when the National Health Interview Survey (NHIS) first asked about colorectal cancer screening, 15.8% of blacks and 22.4% of whites reported having completed a FOBT in the last 3 years (39). Analysis of the 2000, 2003, and 2005 Medicare Current Beneficiary Surveys (MCBS) found that black beneficiaries were less likely than whites to be up-to-date with either FOBT or endoscopic screening, and that these differences could be accounted for by differences in education, income, marital status, type of health insurance, usual place of health care, and self-reported general health status (40). Three studies of colorectal cancer screening in 2001 to 2010 also found that blacks were less likely to be up-to-date with screening than whites, and that these differences could largely be accounted for by differences in education, income, and health insurance (40–43). Analysis of 2010–2013 NHIS data found that the percentage of adults 50 to 75 who were up-to-date with colorectal cancer screening was lower for blacks [56.8%; 95% confidence interval (CI), 54.4%–59.0%] compared with whites (59.8%; 95% CI, 58.8–60.8; ref. 44). Analysis of 2012–2014 Behavioral Risk Factor Surveillance System (BRFSS) survey data found similar rates of being up-to-date with screening for blacks (67.5%; 95% CI, 66.6%–68.5%) and whites (67.1%; 95% CI, 66.8%–67.4%; ref. 44). A 2014 patient survey found that blacks were more likely than whites to be up-to-date with screening (45). In this study, blacks were somewhat more likely to be insured than whites (77.8% vs. 75.5%). Analysis of BRFSS data demonstrates steady increases in the percentage of both blacks and whites who are up-to-date with screening, with black/white differences narrowing until 2014 when increases stalled among blacks but continued among whites (46).

Receipt of colorectal cancer screening is a simpler outcome than being up-to-date with screening, because it is based solely on test completion and not on past testing. Studies examining receipt of screening were based on randomized controlled trials, claims, or electronic health record (EHR) data.

Evidence about black versus white differences in receipt of colorectal cancer screening is mixed. The National Colonoscopy Study (47) found no significant difference in the likelihood of undergoing screening colonoscopy for black and white participants (32). A study of patients insured by TRICARE in 2010–2013 found that blacks were more likely than whites to be screened (48). Analysis of data from the Accelerating Data Value Across a National Community (ADVANCE) network of community health centers found no black/white differences in receipt of FOBT from 2012 to 2015 (49). However, during approximately the same time period the Population-based Research to Optimize the Screening Process (PROSPR) study, which focused on members of a managed care organization, found that black patients were significantly less likely than white patients to complete colorectal cancer screening, including follow-up colonoscopy when indicated (50).

Three studies estimated black/white differences in receipt of follow-up colonoscopy after an abnormal referral test and estimated differences after adjusting for age, sex, comorbidity, and personal history of colon polyps (among other factors). The Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial used flexible sigmoidoscopy as a referral test and found that black participants were significantly less likely than whites to return for follow-up colonoscopy within 1 year of referral at both the first (31) and second (51) screening rounds. In contrast, among Veterans Health Affairs (VHA) patients in 2009–2011, black patients were significantly more likely than white patients to have follow-up colonoscopy within 6 months of an abnormal stool test (52). Finally, analysis of PROSPR data found that black patients were less likely than whites to have follow-up colonoscopy within 90 days of an abnormal stool test (50).

We found only two studies that focused on racial differences in repeat screening. Black PLCO study participants were significantly less likely than white participants to return for screening 3 to 5 years after a normal screening flexible sigmoidoscopy (60.6% vs. 69.3%; ref. 51). Another study of patients in a managed care setting found no evidence of black/white differences in return for surveillance colonoscopy within 3.5 years of an index colonoscopy with high-risk findings (53).

We found evidence that black people have had lower rates of colorectal cancer screening than whites. Survey data, which include repeated cross-sectional sampling of the U.S. population across multiple years, indicate potential narrowing of black/white differences over time. Evidence of black/white differences in screening rates from studies of patient populations, primarily based on claims and EHR data, is mixed. The combined evidence across these studies indicates that at least until the recent past, blacks were less likely to be adequately screened for colorectal cancer than whites and that socioeconomic factors, including health insurance, factor into these disparities. For example, although the PLCO trial covered the cost of the initial screening flexible sigmoidoscopy, it did not cover the cost of follow-up colonoscopy after an abnormal screening test, and this may have contributed to lower rates of follow-up colonoscopy in black study participants (31). Only studies that examined black and white patients who had similar rates of insurance found blacks more likely to be screened than whites (45, 48, 52).

The existence of racial disparities in colorectal cancer screening utilization does not rule out the potential for racial differences in colorectal cancer risk. If there are racial differences in colorectal cancer risk, then there should be evidence of differences in observable markers of the underlying disease process. These markers include adenoma prevalence and differences in adenoma size or histology, which could indicate differences in the rate of progression from a precursor lesion to cancer.

Table 2 compares findings at screening for black and white participants, including the unadjusted percentages of participants with outcomes of interest and ORs or RRs that estimate the strength of the relationship between race and screening outcomes. We include aORs and aRRs, though each study adjusted for somewhat different factors. Studies generally reported more than one outcome of interest. Findings by outcomes are summarized below. Consistent with the literature, we define advanced adenomas as adenomas that are ≥10 mm or have high-grade dysplasia or villous histology.

We found mixed evidence that adenoma prevalence differs for black and white people. Of eight studies that described racial differences in adenoma prevalence at screening colonoscopy, four estimated higher adenoma prevalence in blacks than whites (38, 54–56), two estimated similar adenoma prevalence in blacks and whites (32, 57), and two estimated lower adenoma prevalence in blacks than whites (58, 59). The study that found the strongest evidence of higher adenoma risk in blacks relative to whites (aRR = 1.76) estimated that adenoma prevalence was 2.7 percentage points higher in blacks than whites among participants 50 to 59 years old, 10.3 points higher among participants 60 to 69 years old, and a 13.6 points higher among participants 70 and older (54). The PLCO study found no detectable black versus white differences in adenoma prevalence among study participants who underwent follow-up colonoscopy, at either the first (31) or second screen (51), though only patients with abnormal findings at flexible sigmoidoscopy were referred to colonoscopy. Pooled analysis of data from three colorectal cancer chemoprevention studies, each with null findings, found no black versus white differences in adenoma prevalence at surveillance colonoscopy (60).

We found mixed evidence for racial differences in risk for advanced adenomas. Two of seven studies that described racial differences in advanced adenoma prevalence at screening colonoscopy observed a higher prevalence of advanced adenomas in black patients (32), whereas five found that blacks had similar or lower risk of advanced adenomas than whites (55–57, 59, 61). Two of three studies that reported aRRs (or aOR) of advanced adenomas in black versus white study participants at screening colonoscopy estimated an elevated risk of advanced adenomas in black participants (54), including one study that found black women were at greater risk of advanced adenomas than white women, but black men were at lower risk of advanced adenomas than white men (61). The PLCO study found no racial differences in the prevalence of advanced adenomas detected at the follow-up colonoscopy after the first flexible sigmoidoscopy screening (31), but analysis of the second screening that controlled for screening center found evidence that blacks had a higher prevalence of advanced adenomas than whites (51). Two studies of surveillance colonoscopy each found that blacks were more likely to have advanced adenomas than whites (60, 62).

The location of adenomas is important because adenomas in the proximal colon may be more difficult to detect (63) and proximal cancers may have a lower 5-year survival rate than distal colon and rectal cancers due to differences in disease characteristics (64, 65). Consistent with the literature, we use proximal location to indicate the transverse colon, hepatic flexure, ascending colon, and cecum.

We found mixed evidence for racial differences in the prevalence of proximal adenomas based on results from three observational studies (38, 55, 58). One study found similar proximal adenoma prevalence in black and white patients (55). Another study found that blacks were significantly more likely to have proximal adenomas compared with whites, adjusting for only age and family history of colorectal cancer (38). The third study found that proximal adenoma prevalence was lower in black patients than in white patients (58). Finally, the PLCO study found that black and white study participants had similar odds of having a proximal adenoma detected at follow-up colonoscopy at both the first and second screening (3 to 5 years later), though only participants with findings at flexible sigmoidoscopy were referred to colonoscopy (31, 51).

Evidence about the relationship between race and prevalence of advanced proximal adenomas was limited and mixed. An observational study carried out in Boston Medical Center safety-net clinics found that black and white patients had the same prevalence of advanced proximal adenomas (61). In contrast, the PLCO study found that black participants were more likely to have advanced proximal adenomas than white participants (31, 51). Estimated racial differences were observed at the first and second rounds of screening, but only reached statistical significance at the first round.

Interval colorectal cancer refers to colorectal cancer detected after colonoscopy and before the next recommended screening exam (66). Analysis of SEER-Medicare data, based on 66 to 75 year olds who underwent colonoscopy between 2002 and 2011, found that black patients were at significantly greater risk of interval cancer than white patients; the estimated probability of an interval cancer up to 54 months after colonoscopy was 0.071 for black patients and 0.051 for white patients (67). Interval cancers can be attributed to provider characteristics (adenoma detection rates, rates of complete adenoma/serrated polyp resection), patient characteristics (adequate bowel cleansing), and disease characteristics (progression rates). Thus, it is unclear what drives differences in interval cancer rates.

We found mixed evidence for racial differences in the prevalence of adenomas and limited evidence that black people may be at greater risk for advanced and proximal adenomas compared with whites. Our findings are similar to results from a recent systematic review and meta-analysis of nine studies that found no difference in the prevalence of advanced adenomas in black (6.6%) and white (6.2%) people but did find evidence that blacks had a higher prevalence of advanced proximal adenomas than whites (3.3% vs. 2.4%; ref. 68).

It is difficult to draw conclusions about racial differences in adenoma risk in the context of screening disparities. Colonoscopy with polypectomy has long-term effects on adenoma prevalence. If whites are more likely to be screened than blacks, this could result in underestimation of both adenoma and advanced adenoma prevalence in whites compared with blacks, even in studies that focused on screening outcomes. For example, in a study that described black/white differences in adenoma prevalence by age, differences were small before age 60, when people are less likely to be previously screened, and large after age 60 when the chance of previous screening increases, especially among whites (54). On the other hand, if black people receive lower-quality colonoscopy than whites, this could result in underestimation of adenomas and advanced adenomas in blacks compared with whites. Within the PLCO study, racial differences in the prevalence of abnormal findings at the second screening flexible sigmoidoscopy were partly explained by black patients being more likely to have their colonoscopies at centers with lower adenoma detection rates (51).

Understanding what drives racial disparities will better equip us to address them. Disparities that are driven by disparate access to quality care point to the importance of improving access to and uptake of high-quality screening. Disparities that arise from disparate risk point to the need for more aggressive screening in higher-risk groups, including earlier initiation and shorter screening intervals, and further exploration of factors that drive increased risk. Based on available data, we found strong evidence for racial differences in colorectal cancer screening access, but limited evidence for racial differences in adenoma prevalence. In general, black and white patients who are screened have similar adenoma prevalence. Although there is some indication that risk of advanced and proximal adenomas is higher in black than white people, these differences could be driven by differences in screening. Based on this review, we conclude that higher rates of colorectal cancer incidence among black patients are largely due to lower rates of screening.

Screening can reduce colorectal cancer incidence and mortality, but black Americans face greater barriers to screening than whites (69). In 2017, black adults younger than 65 were less likely than whites to have health insurance (85.9% vs. 91.5%; ref. 70), and people without health insurance are less likely to participate in colorectal cancer screening (71). Racial barriers persist among the insured, where healthcare systems and physicians within these systems play an important role in promoting colorectal cancer screening. In spite of widespread knowledge that blacks have higher colorectal cancer incidence than whites, blacks are less likely than whites to receive a recommendation for colorectal cancer screening (72, 73). Physicians are less likely to recommend screening based on their perception of a patient's ability to pay (74). Physicians are also less likely to recommend colorectal cancer screening when they identify a shortage of specialists in the region, and blacks may be more likely than whites to live in such regions (75). There is also evidence that black patients receive colonoscopies from physicians with lower adenoma detection rates than white patients (51, 67, 76). From the patient perspective, trust in an individual's primary care provider is the most important factor in the decision to undergo colorectal cancer screening, and the degree to which trust plays a role in the decision varies across different racial and ethnic groups (77).

Our report has several important limitations. This narrative review lacked the rigor of a systematic review, and we do not provide pooled estimates of screening outcomes. We described differences in colorectal cancer screening and risk for black and white patients within the United States and did not address differences across other racial or ethnic groups or in other countries. In addition, because of wide heterogeneity in genetics and ancestry for both “blacks” and “whites” in the United States, comparisons between these groups could mask true risk differences in more homogeneous genetic subgroups. We relied primarily on adenoma prevalence as a proxy for underlying colorectal cancer risk. We did not address racial differences in the molecular characteristics of detected lesions which may be related to differences in disease progression and survival after diagnosis. Nor did we examine differences in the prevalence of sessile serrated polyps, which could be related to differences in the effectiveness of screening, and both colorectal cancer incidence and mortality (78). Finally, there is potential for bias in study estimates, especially from observational studies. In particular, black/white differences in screening uptake could result in differential underestimation of adenoma and advanced adenoma prevalence, and people at increased risk of colorectal cancer due to modifiable risk factors, such as smoking, may be underrepresented in studies of screened populations. In spite of these limitations, we feel that the available research, taken together, provides a compelling argument that the higher colorectal cancer incidence observed in blacks relative to whites is primarily due to differences in screening utilization.

It is imperative that we seek ways to reduce racial disparities in colorectal cancer screening, but how? Multilevel solutions are needed, including national and state policies, to improve access to screening and follow-up of abnormal screening tests, health systems solutions to promote screening, and patient education efforts (79). Healthcare organization can ensure that testing is accessible by mailing FITs to all patients (80) and using patient navigators to assist patients (12, 81). Overall, our review suggests that equal access to care can reduce screening disparities.

C.M. Rutter and K.E. Bouskill reports grants from NCI (U01CA199335) during the conduct of the study. A.B. Knudsen reports grants from NCI and grants from American Cancer Society during the conduct of the study. J.S. Lin reports other from AHRQ (contract to support the USPSTF, funds to institution) during the conduct of the study.

The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the National Cancer Institute or the American Cancer Society.

Research reported in this publication was supported by grant number U01CA199335 (C.M. Rutter, A.B. Knudsen, and K.E. Bouskill) from the NCI as part of the Cancer Intervention and Surveillance Modeling Network (CISNET) and by a Research Scholar Grant from the American Cancer Society under award number RSG-15-002-01-CCE (A.B. Knudsen). We also want to thank Jody Larkin for assistance with literature searches and Claudia Seguin for creating figures showing colorectal cancer incidence by race, age, and time period.