We observed a lower rate of diagnostic evaluation following an abnormal screening FSG among blacks as compared with whites. This lower rate of follow-up evaluation for screen-detected abnormalities implies that the reported racial disparity in colorectal cancer may not be eliminated by a universal screening program if a separate follow-up diagnostic testing is required. Overall, we did not observe any meaningful difference in the yield of colorectal neoplasia by race. This suggests that the biology of colorectal cancer may not be materially different by race, at least in the early stages of carcinogenesis, but instead that health-care utilization differences among the races may play a more important role in the observed disparities in colorectal cancer.
Although we did not observe any difference in the overall prevalence of adenoma in the proximal colon by race (RR = 1.09, 95% CI = 0.91 to 1.29), we found a higher prevalence of proximal advanced adenomas among blacks (RR = 1.56, 95% CI = 1.13 to 2.14). However, this finding was inconsistent across education groups. We observed a higher risk of proximal advanced adenoma among blacks with high school education or less (RR = 1.90, 95% CI = 1.21 to 3.00) and postgraduate education (RR = 2.96, 95% CI = 1.55 to 5.66) compared with their white counterparts, but not in the group with college education (RR = 0.85, 95% CI = 0.44 to 1.65). Although this may suggest biological differences, it could also be related to the small sample sizes in these categories or residual confounding. Regardless, our study does not provide any strong evidence to support a different colorectal cancer screening recommendation for blacks.
Our results are comparable to the report of similar colorectal cancer survival between blacks and whites in the US Veterans Affairs Health Care System (26
), where access to health-care resources is equivalent. A similar finding was also reported among participants in a randomized clinical trial of adjuvant chemotherapy (27
), which reported no difference in 5-year disease-free survival between whites and blacks (58% vs 57%) nor in overall survival (66% vs 65%). These findings suggest that differences in access and utilization of health-care resources may in part explain the lower survival in blacks with colorectal cancer. Studies have shown that minority populations are less likely to use health-care resources even in an equal access environment (28
It is uncertain what factors are directly responsible for the lower rates of follow-up for abnormal testing among blacks, but a number of factors could be considered. Low socioeconomic status may affect health-care utilization because of the direct cost of care such as co-pay or indirect cost such as lost wages while accessing health-care resources. It is possible that the need for multiple tests following abnormal PLCO screening may adversely affect the ability of some subjects to undergo follow-up testing. Lack of knowledge of cancer prevention may contribute to low uptake of diagnostic testing, and lack of cultural competence on the part of care providers may also constitute a barrier to health-care utilization (31
In general, our study demonstrates that blacks were less likely to undergo diagnostic evaluations following an abnormal screening FSG compared with their white counterparts at every level of education, but this reached statistical significance only among participants with high school education or less. It is quite possible that our findings of lower health-care utilization among blacks may actually be an underestimation. Black participants in the PLCO were more educated and health conscious than comparable members of the general population (34
) and were encouraged to undergo follow-up evaluations by virtue of being enrolled in an ongoing clinical trial. Therefore, the fact that even these study participants who had abnormal screening tests did not undergo appropriate diagnostic evaluations, would suggest that utilization of health-care resources in the general population may be lower than what we captured in our study.
We are not aware of any study that has examined the use of diagnostic evaluation after screening and yield of colorectal neoplasia by race for direct comparison. However, three large studies recently compared the prevalence of colorectal neoplasia during screening colonoscopy using the Clinical Outcomes Research Initiative database, an endoscopic data repository of geographically diverse gastroenterology practices in the United States. Two of these studies did not use histopathologic diagnosis. Thornton et al. (11
) reported an increased odds of proximal polyps in blacks (OR = 1.30, 95% CI = 1.11 to 1.52) compared with whites, whereas Lieberman et al. (12
) reported an increased odds of large (>9 mm) polyps among blacks but similar odds of proximal large polyps (OR = 1.13, 95% CI = 0.93 to 1.38). The third study (35
) used the histopathologic diagnosis of detected polyps from the Clinical Outcomes Research Initiative database and reported an increased odds of advanced adenoma among blacks (OR = 1.35, 95% CI = 1.04 to 1.75), which is at variance with our findings. However, those authors also reported no difference by race and/or ethnicity in the prevalence of advanced histology in adenoma, either with size less than 10 mm in diameter or with size more than 10 mm in diameter (35
). The difference in the findings between that study and our own may be because serrated histology was included as advanced pathology in the other study. Another difference is that our study used a multilevel screening strategy in which only subjects with abnormal FSG results had colonoscopies rather than the entire screened population.
The strengths of our study are that we prospectively evaluated both utilization of health-care resources and the yield of colorectal neoplasia by race. Our study population was from an ongoing, large, community-based screening trial recruited from 10 geographically dispersed centers. Also, the diagnostic colonoscopies were arranged by participants’ physicians and performed by the community gastroenterologists whom their physicians chose. This enables our study to closely reflect what might happen in a real-world scenario.
Our study also has limitations. Blacks were underrepresented in the PLCO trial despite intense efforts during recruitment. The enrollment was 5% for blacks in PLCO as compared with an age-eligible US population that was 9.5% black. Participants in the PLCO are also more educated, more likely to exercise regularly, and less likely to be current smokers than comparable members of the general public (18
). Hence, the yield of colorectal neoplasia may be lower compared with the general population. However, we do not believe that this should differentially affect the blacks as compared with whites in our study. The racial difference in the rates of follow-up for abnormal screening (an endpoint of our study) may mask differences in the yield of colorectal neoplasia because of incomplete ascertainment, and we used the highest education attained as a proxy for socioeconomic status. Furthermore, participants with proximal colon neoplasia but without any distal lesions would not be detected because the participants who were referred for colonoscopy had distal colon lesions. Therefore, if blacks were more likely to have isolated proximal advanced adenoma compared with whites, this would not be captured in our study. This should be a focus of future studies. Proximal advanced adenoma has been estimated to occur in 1.5%–2.7% of subjects without any distal colon polyps in colonoscopy-based screening studies (36
). Of note, Thornton et al. (11
) suggested that blacks have a higher rate of isolated proximal polyps, but the study lacked histopathologic diagnosis. Also, in an epidemiological necropsy study of 3558 persons (aged 20–89 years) in a single referral center of whom 26% died from malignancy, Pendergrass et al. (38
) reported a higher prevalence of adenoma among young whites (aged 20–49 years) compared with young blacks (ie, 2.52 vs 1.97 per hundred; RR = 1.28, 95% CI = 1.26 to 1.31) but noted a higher right-to-left ratio in adenoma prevalence among young blacks.
It is noteworthy that our study was not designed to address the recommendation by the American College of Gastroenterology that blacks be screened for colorectal cancer starting at 45 years of age. We evaluated the differences in health-care utilization and biological outcomes (in terms of colorectal neoplasia) by race. Our study suggests that among whites and blacks aged 55–74 years, biological differences may not be as important as health-care utilization as a factor for racial disparity in colorectal cancer. We have no data on racial disparity between the ages of 45 and 54 years, but it is unlikely that the entire population of blacks would have increased risk compared with whites at age 45–54 and then not at age 55–74. However, there may be a subpopulation of blacks who are at increased risk at a younger age.
In conclusion, we did not observe meaningful differences in the yield of colorectal neoplasia by race among participants with diagnostic colonoscopy, but blacks were less likely to undergo diagnostic evaluation following abnormal screening when compared with whites. Targeted interventions aimed at increasing the uptake of screening among minority populations, and provision of an adequate diagnostic component for screening programs is essential if colorectal cancer disparities were to be eliminated.