Prostate-Specific Antigen Levels are Higher in African-American Than in White Patients in a Multicenter Registration Study: Results of RTOG 94-12

Abstract

Purpose: To compare serum prostate-specific antigen (PSA) levels in a national sample of African-American and white men with prostate cancer, and to attempt to explain any differences by using self-reported individual-level socioeconomic status adjustments. Methods and Materials: During 4 1 2 months in 1994–95, 709 patients with nonmetastatic prostate cancer were enrolled in this prospective study; 17.5% were African-American and 82.5% were white. Information about clinical stage, tumor grade, pretreatment PSA, type of insurance, and educational and income status was obtained. Serum PSA levels were measured and racial differences were found; how the differences were influenced by other patient- or tumor-related factors and if the differences could be explained by socioeconomic status disparities were determined. In univariate analyses, factors associated with the mean PSA levels were studied; log-converted values were used to yield a normal distribution. Multivariate analyses were done on log-linear models for description of association patterns among various categorical variables; a perfectly fitted model should have a correlation value (CV) of 1.0. Results: The mean PSA level was higher in African-Americans (14.68 ng/ml) than in whites (9.82 ng/ml) ( p = 0.001). Clinical stage ( p = 0.001), Gleason sum tumor grade ( p = 0.0001), educational level ( p = 0.001), and household income ( p = 0.03) were also associated with mean PSA levels; age, type of biopsy, and insurance status were not. Disease stage ( p = 0.0001), grade ( p = 0.0001), education ( p = 0.07), and income ( p = 0.02) were all associated with PSA levels for whites, but none of these factors were important for African-Americans (all p values > 0.1). The best fitted log-linear model (CV = 0.99) contained PSA (< 10, 10–20, and > 20), Gleason sum grade (2–5, 6–7, and 8–10), race, and two interactions: PSA by race ( p = 0.0012) and PSA by Gleason sum ( p = 0.0001). Models replacing race for either income (CV = 0.82) or education (CV = 0.82) or both (CV = 0.78) did not fit as well. Conclusions: African-Americans with nonmetastatic prostate cancer have higher serum PSA levels at diagnosis than whites, implying a higher tumor cell burden. Individual-level household income, education, or insurance status alone or in combination account for racial differences, but only partially.