A subgroup analysis of the phase III trials of Provenge (Sipuleucel-T) suggests that there might be a dramatic role for Provenge in African-American men who have advanced prostate cancer that has become castration-resistant (mCRPC).

The analysis, which was released at the American Urological Association 2012 Annual Scientific Meeting, was headed up by Colonel David G. McLeod, MD, chief of Urologic Oncology at Walter Reed Army Medical Center in Washington, DC.
McLeod conducted a subgroup analysis of black men who had been enrolled in the initial three phase III clinical trials of sipuleucel-T. Their find is significant because prostate cancer is more common in black men than white men and tends to be more aggressive in black men (it has a higher rate of metastatic spread (4:1) in African Americans versus Caucasian men).

Originally, Provenge was approved for metastatic prostate cancer on the basis of the phase III IMPACT study. At a median of 34 months of follow-up, Provenge was associated with a 22% reduction in mortality risk (hazard ratio [HR] = 0.78; 95% CI, 0.61-0.98; P = .03), a 4.1-month improvement in median overall survival (OS) of 25.8 versus 21.7 months, and an estimated 3-year survival of 31.7% versus 23% in the Provenge versus control group, respectively.

Of a total of 737 patients in the phase III studies, 488 were randomized to receive Provenge and 249 to placebo. Thirty three (33) of the men who were in the group that received Provenge were African-American while ten (10) African American men were in the placebo group.

The results for the African American men were dramatically different than the general overall results. The African American men assigned to Provenge achieved a median OS of 45.3 months versus 14.6 months in control patients (HR = 0.288; 95% CI, 0.125-0.662; P = .003), which represents a 30.7 -month difference between the two treatment arms. Yes, let me repeat that, there was a 30.7-month survival benefit for African American men who received Provenge.

Irrespective of race, there was a consistent survival benefit for all men assigned to Provenge therapy versus the men assigned to placebo.

These results are preliminary, given that the phase III studies enrolled only a small number of black men and because these results came from a retrospective analysis.

McLeod DG, Quinn DI, Cullen J, Whitmore JB. Sipuleucel-T in African Americans: a subgroup analysis of three phase III trials of sipuleucel-T in metastatic castrate resistant prostate cancer. Presented at the American Urological Association Annual Meeting; May 19-23, 2012; Atlanta, GA. Abstract 953.

Joel T. Nowak, M.A., M.S.W.