Conquering cancer disparities: new opportunities for cancer epidemiology, biomarker, and prevention research.

Cancer disparities represent a significant public health problem in the United States. Inequity in cancer screening, incidence, treatment, prognosis, and mortality is a hallmark of many common cancers (1). These disparities exist across groups defined by race, ethnicity, gender, age, and socioeconomic status. For example, African American men have a 34% greater prostate cancer–specific incidence and 123% greater prostate cancer–specific mortality than European American men (2). The greater disparity in mortality relative to the disparity in incidence suggests that factors related to biology, behavior, social circumstances, access to care, and other postdiagnosis factors influence clinical outcomes beyond those that contribute to disease etiology. Elimination of cancer disparities is also a critical public health need: Woolf et al. (3) estimated that the complete elimination of health disparities (including but not limited to cancer disparities) during the 1990s would have saved five times more lives than were saved by technological innovations in health care over the same period. The kind of disparities observed for prostate and other cancers probably involves the complex interaction of many factors acting less favorably in specific groups over the lifetime of the individual. To illustrate this hypothesis, Table 1 presents information about the continuum of disease from preneoplastic to preclinical to clinical prostate cancer. Data obtained from autopsy studies (4-6) indicate that rates of high-grade prostatic intraepithelial neoplasia and prostate cancer are slightly higher in African American men compared with European American men, and this disparity is greatest in the age range 40 to 60 years. This is consistent with the observation that prostate cancer occurs at a slightly earlier age in African American men compared with European American men (7). This disparity persists when measured by Surveillance, Epidemiology, and End Results incidence and mortality rates (Table 1). The disparity in diagnosed prostate cancer again peaks in the age range 40 to 60 years, and shows a much greater disparity in mortality than in incidence. These data suggest that African Americans are at greater risk and have poorer outcomes for prostate cancer at most ages, and that this disparity increases across the continuum of disease from latent high-grade prostatic intraepithelial neoplasia to subclinical disease to clinically apparent disease to mortality. One interpretation of the example cited above is that prostate cancer disparities are caused by innate biological susceptibility in conjunction with environmental exposures that accumulate over time to confer prostate cancer risk. Furthermore, unfavorable social influences, physical environment, or health care experiences may accumulate to confer poorer outcomes from prostate cancer in African American men compared with European American men. This hypothesis is consistent with reported differences in individual prostate cancer risk factors (8), screening (9), and treatment (10) between African American and European American men. Therefore, disparities in prostate cancer are likely to reflect the complex, multifactorial influences of biological, social, environmental, behavioral, health care, and cultural factors. These data also imply that prostate cancer disparities arise early in the process of carcinogenesis and that they persist across time with the accumulation of disparate exposures to factors associated with cancer risk. Finally, these data suggest that an appropriate focus of research on disparities could be relatively young African American men (e.g., ages 40-60 years), as disparities are already apparent before the majority of prostate cancer is clinically evident.