Survival In Men With Metastatic Prostate Cancer

Results of Southwest Oncology Group (SWOG) study (8894), a randomized, prospective phase III trial comparing orchiectomy and anti-antigen with orchiectomy and placebo in men with metastatic prostate cancer provided an opportunity to analyze the difference in survival among men with metastatic disease by ethnic background in a rigidly controlled treatment regimen. The large sample size and the lack of uncontrolled variables made this trial a good setting for evaluating whether differences in survival between African American men and Caucasian men can be explained by differences in prognostic variables or whether there may be a difference in the biological activity of meta-static prostate cancer among African American men. Using data from 288 African American men and 975 White men in the trial, they conducted a proportional hazard regression analysis to determine if ethnicity was an independent predictor of survival. The study was double blinded and the primary end-point of the study was death from any cause, with the secondary end-point being progression-free survival.

No differences were noted in treatment assignment by ethnicity: 49.3% African American men and 50.2% of White men were randomly assigned to receive flutamide. The results of the study show that, compared to White men in the study, African American men in the study were generally younger, had higher PSA levels, more extensive disease, higher Gleason scores, more frequent bone pain and a worse performance status. African American men in the study also had poorer survival than White men in the study, perhaps because of their later stage of diagnosis. Of the 198 African American and 719 White men for whom complete information about covariants was available at study entry, the median survival is 26 months and 35 months, respectively (a log rank test, P=0.001).

To determine whether the poorer survival among African American men relative to White men was a reflection of the poor prognostic factors, they controlled for the effect of these factors in a multivariable proportional hazard regression model. After adjustment for the potential confounding variables, the African American patients had a hazard ratio for death relative to White patients of 1.23 [95% confidence intervals (CI) = 1.042-1.47], and this increase risk was statistically significant (P = 0.018). The likelihood ratio test for the addition of the ethnicity to the model with other prognostic variables showed that the effect of ethnicity was statistically significant. The conclusion of this study was that African American men with metastatic prostate cancer have a statistically significant worse prognosis than White men that cannot be explained by the prognostic variable explored in this study. Further, they state that their data suggest that the existence of ethnic differences in the biology of the disease may be the cause for these outcomes and should be further investigated.28

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