Despite improvements in treatment, standard of care, and screening options, studies indicate that racial disparities persist in CRC incidence, mortality, and survival. The age-adjusted CRC mortality trends by race have followed a relatively divergent pattern for over twenty years. While the rates for Caucasians have slowly but steadily decreased, those for African-Americans have been relatively stable over time [46
]. Based on SEER data, between 1980 and 2000, the age-adjusted mortality rate decreased 7.9% among Caucasians and only 0.5% among African-Americans [46
]. This racial disparity in CRC mortality is a reflection of incidence and survival, as African-Americans have the highest incidence rates and lowest survival rates for cancer of the colon and rectum among all racial and ethnic groups in the United States [2
Previous publications have offered a wealth of possible reasons that may explain the racial disparity in CRC survival. These include varied screening patterns [31
] that result in disparate disease stages [8
] at diagnosis, comorbid conditions [21
], histologic type [53
], tumor grade [39
], quality of and access to care [12
], follow-up surveillance [49
], biological variability [15
], clinical under-staging [8
], and differences in treatment offered or accepted [11
] including racial differences in the compliance of treatment regimens. In addition, socioeconomic [9
] and sociodemographic [47
] factors including education [12
], religious involvement and social support [63
], poverty level [12
], insurance status [16
], physical activity, obesity, and attitudes and beliefs [65
] about cancer fatalism [66
] may contribute to CRC racial disparities in survival.
In the vast majority of CRC studies, a greater proportion of African-Americans were diagnosed with advanced stage CRC compared with Caucasians [6
]. This is of great concern since pathologic tumor stage is the single most powerful prognostic indicator of CRC [67
], although several studies have reported that race is a stage-independent prognostic factor of CRC [4
]. One of the many possible explanations for the discrepancy in stage distribution by race is that Caucasians are more likely to have early stage (localized) disease detection in screening tests, and in contrast; African-Americans are more likely to have symptomatically detected late stage (distant) tumors. Cooper et al. [49
] found that colonoscopy, sigmoidoscopy, and fecal occult blood tests were performed more commonly in Caucasians for screening and surveillance purposes, however, colonoscopies were performed more often in African-Americans for diagnostic purposes. A delay in the use of screening procedures for colorectal cancer until signs or symptoms develop may contribute to the disparate proportion of late stage tumors among African-Americans. In addition, African-Americans are more likely to be diagnosed at a younger age and with proximal (right-side) tumors compared with Caucasians [11
]. Consequently, the American College of Gastroenterology’s Committee of Minority Affairs and Cultural Diversity has issued new screening recommendations to African-Americans that include “first line” colonoscopy screening at the age of 45, rather than age 50 [27
]. The use of colonoscopy is likely to improve overall detection rates including right side tumors of the colon that cannot be reached by flexible sigmoidoscopy [27
Several factors may influence delays in the use of screening options and medical procedures, including education, social support, poverty, and diminished access to health and medical services and refusal of treatment [9
]. Mandelblatt et al. [14
] observed that even among all persons living in the poorest socioeconomic status area, African-Americans continued to have significantly higher rates of late stage disease than Caucasians (OR = 1.24, 95% CI: 1.13–1.36). Kinney et al. [63
] examined the relationship between social ties and the risk of colon cancer stage at diagnosis, and found that among African-Americans, minimal social support was associated with risk of both local (OR = 3.69, 95% CI: 1.08–12.69) and advanced (OR = 5.10, 95% CI: 2.03–12.82) stage disease. Robinson et al. [69
] assessed cancer awareness among African-Americans and found that they were less knowledgeable than Caucasians with regard to treatment modalities, and were more likely to perceive surgery as contributing to metastases.
Even though African-Americans tend to be diagnosed with a later stage of disease than Caucasians, a greater disparity in survival is found at an earlier stage of disease (i.e., stage II) among these two racial groups than at later stages of disease (). This early stage disparity persists even after analyzing patients who received surgical resection as their only treatment procedure. The role of adjuvant therapy in patients with stage II CRCs remains controversial [73
], however, African-Americans with specified clinicopathological characteristics, such as high-grade tumors, may benefit from adjuvant chemotherapy. Future research in this important clinical area is recommended.
We examined the degree of CRC racial disparity in survival and mortality according to study population data source. Overall, the greatest disparities have been found in non-VA hospital-based and university-based studies (). Lesser racial disparities exist in SEER and other population-based cancer registry studies and health care coverage database studies, and minimal disparities were found in studies of patients within the VA medical system. The precision of associations was greatest among the SEER and VA studies, which consisted of large sample sizes (, ).
Relative risks of colorectal cancer mortality for African Americans compared with Caucasians, based on data source of study.
Findings from some studies have indicated that quality of care and equal access to care result in similar mortality experiences by race [24
]. This is evident among studies in which patients are equally insured or are in an equal access medical system such as that of the VA integrated health care program. The case mix from the VA system is relatively more homogeneous with respect to sociodemographic confounding variables compared with the general population [70
]. Despite homogeneity in terms of equal access care, insurance status, treatment, and social factors, an increased risk of mortality among African-Americans has been observed [24
], albeit an attenuated magnitude of risk compared to non-VA studies. Because of the potential intrinsic population similarities within the VA medical system, the generalizability (external validity) to the US population is limited. Furthermore, the majority of VA patients are men. Other potential shortcomings of using the VA database may include a lack of information pertaining to clinical detail, care received in other institutions may not be captured in the VA system, and missing information based on the use of Veterans Health Administration data [71
]. In addition, reported associations in these studies were generally not stage-specific, thus, interpretation of racial disparities by stage is limited.
Based on SEER data, African-Americans are generally considered to have an approximately 20% increased risk of CRC mortality compared with Caucasians. Large scale population-based studies serve to provide descriptive statistics pertaining to CRC survival on the aggregate level. In some studies of this nature, it is not feasible to ascertain information on detailed clinical and pathological characteristics or data on treatment in terms of receipt and compliance. Therefore, findings from these studies may not offer patient specific prognostic patterns in the clinical setting, but do offer descriptive insight to nationwide disease patterns. Not all SEER studies are limited in patient information, however. A unique feature of SEER registry data is that patient data can be linked with medical coverage databases, and the SEER database can be sampled and merged with more informative patient medical records. Potosky et al. [29
], for example, sampled from the SEER database and identified treating physicians in order to verify the use of chemotherapy and radiotherapy. Augmenting SEER data with more detailed clinical information may increase study validity by the ability to control for potential confounding factors.
In university-based and non-VA hospital studies, African-Americans generally have a greater risk of CRC mortality than what is typically observed in other studies. This may in part, be explained by more efficient control of confounding factors compared to large population or registry based research. University and non-VA-based studies usually entail comparatively smaller sample sizes that allow feasible data ascertainment directly from medical records, physician charts, and surgical pathology reports. This type of data extraction increases the internal validity of study findings since detailed and objective clinicopathological information can be directly obtained to evaluate the study hypothesis. In contrast, studies that rely solely on data for administrative purposes may be relatively more susceptible to coding errors or problems with missing data [24
]. Limitations from university and hospital-based studies may include less precise findings due to comparatively small sample sizes, and findings from single institution studies may only be generalizable to limited populations due to the study sample being drawn from specific hospital catchment areas.