This study is the largest prospective study to examine the association of socioeconomic indicators and health care resources with prostate cancer risk among African-American and Caucasian men. We found differential effects among African-Americans and Caucasians for certain SES indicators and increased risk of advanced prostate cancer, with the strongest association being observed for African-American men living in counties with fewer urologists. These results suggest that the ratio of urologists to population may be associated with reduced prostate cancer risks and may play a role in the variation in rates observed between African-American and Caucasian men.
Our findings are supported by those of recent cancer registry studies. Oliver and colleagues observed that poverty and residing in areas with fewer physicians were associated with a decreased incidence of any prostate cancer among Caucasians but not African Americans in Virginia (11
). Advanced stage prostate cancer was associated with lack of health insurance in a national hospital-based cancer registry comprised of predominantly Caucasian patients (OR=1.85, 95% CI=1.69, 2.03) (21
). Although prostate cancer severity (i.e., tumor Gleason score ≥ 7) was associated with neighborhood socioeconomic deprivation among African-American patients (OR=1.71, 95% CI: 1.21, 2.40, highest versus lowest quartile) and Caucasian patients (OR=1.34, 95% CI: 1.19, 1.52, highest versus lowest quartile) from the Pennsylvania Cancer Registry (22
), no associations were observed between neighborhood deprivation and advanced (high-stage) prostate cancer for African Americans or Caucasians (OR=1.13, 95% CI: 0.77, 1.64 and OR=0.98, 95% CI: 0.82, 1.18, respectively). The estimated risks for advanced stage prostate cancer, however, were similar in magnitude and direction to those observed in the present study. These previous studies were cross-sectional and therefore unable to examine temporal relationships between SES, healthcare availability, and subsequent development of prostate cancer and often restricted to a specific geographic region (e.g., a single state). Studies examining area-level SES or healthcare population density and prostate cancer through the linkage of census or county level data to cancer registries are unable to account for a person’s lifestyle or other individual health risk factors, including family history of prostate cancer.
Other factors that were not assessed in the NIH-AARP study may play a role in the increased incidence of advanced prostate cancer among African Americans residing in areas with fewer urologists. A recent ecologic study suggests that the patterns of urologist density are influenced by factors other than traditional socioeconomic measures, such as climate (23
). In addition, it has been suggested that transportation and longer distance to a urologist may disproportionally impact African-American patients (24
). The lack of a strong association between health insurance and non-advanced prostate cancer in our study may be related to our older participants qualifying for Medicare, as prostate cancer often occurs after age 65 (26
). Our observation that higher neighborhood deprivation was associated with decreased risk among Caucasians was unexpected and may be related to differences in the disease and screening. Because Caucasians are more likely to have indolent disease, it is possible that they are less likely to experience symptoms and therefore, may be less likely to seek screening for prostate cancer; whereas African American men residing in similarly deprived areas may seek out screening since they are more likely to have symptomatic, aggressive disease (6
). Another possibility is that African-American men may be targeted differently by physicians for screening because they are in a high-risk group (27
Among the inherent strengths of the present study is that it is based on a cohort rather than only a case series from cancer registries where in our cohort individual health risk factors were measured and study subjects were then followed forward in time allowing for direct assessment of cancer incidence. The large size of the NIH-AARP Diet and Health Study allowed us to examine potential associations among African-Americans, a high-risk population for prostate cancer. A limitation of our study is that information on household income was not ascertained in the NIH-AARP Study thus limiting our ability to account for individual socioeconomic characteristics beyond education. In addition, the cohort was predominantly older, middle class participants; therefore, results may not apply to other socioeconomically-diverse populations. Our findings may reflect incomplete adjustment for changes in SES, health care availability, and behavioral health risk factors which were not available in our study cohort. Unmeasured area-level characteristics that may play a role in prostate cancer risk include perceived neighborhood safety and social support.
In conclusion, the results of this study suggest that minimizing differences in health care availability is a potentially important pathway to minimizing disparities in prostate cancer incidence. Additional population-based studies are needed to confirm these associations and to examine the potential influence of neighborhood SES and healthcare population density on prostate cancer progression and/or the potential mediating effects of biological and molecular cancer markers.