Monday, May 21, 2012 10:30 AM-12:30 PM
Prostate Cancer: Advanced III
953: Sipuleucel-T in African Americans: a subgroup analysis of three phase 3 trials of sipuleucel-T in metastatic castrate resistant prostate cancer
David G. McLeod
David I. Quinn
James B. Whitmore
Introduction and Objectives
African American (AA) men are disproportionately affected by prostate cancer, with an incidence and death rate of 230.0 and 54.2 per 100,000, respectively, vs 143.8 and 22.8 for Caucasians. Sipuleucel-T is an autologous cellular immunotherapy indicated for the treatment of men with asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer (mCRPC). The objectives of this analysis were to assess the outcomes and product parameters of AA patients (pts) treated in three phase 3 clinical trials of sipuleucel-T.
Among 737 pts (495 events) included in an integrated analysis of data from three phase 3 studies, 488 were randomized to sipuleucel-T (AA, 33; Caucasian, 437; other, 18) and 249 received control (AA, 10; Caucasian, 229; other, 10). Cox proportional hazards regression analysis, stratified by study and adjusted for baseline prostate specific antigen and lactate dehydrogenase, was used to assess the treatment effect on overall survival (OS) in all randomized pts and the AA subpopulation. The Kruskal-Wallis test was used to compare product parameters (total nucleated cell counts, CD54 upregulation and CD54+ cell count) between race groups (AA, Caucasian and other).
Results for the ITT population for the 3 studies demonstrated a positive treatment effect (HR=0.735 [95% CI: 0.613, 0.882]; P <0.001). Difference in median OS was 3.9 months (25.4 months for sipuleucel-T; 21.5 months for control). Results were consistent in the AA subgroup (HR=0.288 [95% CI: 0.125, 0.662]; P = 0.003), despite baseline differences favoring the control arm. Difference in median OS was 30.7 months (45.3 months for sipuleucel-T; 14.6 months for control). Although product parameters trended to be higher in AA, there were no statistically significant differences between race groups. Baseline factors for the AA population relative to the overall population included more exposure to prior chemotherapy, and lower age, baseline hemoglobin, ECOG status and bisphosphonate use. AEs for the AA subgroup were comparable to the overall study population.
While no definitive conclusions can be drawn given the limited sample size, the OS HR for AA was well below that for the overall population, with a 95% CI bounded below 1, suggesting that AA pts with mCRPC benefit from sipuleucel-T treatment, and providing support for further investigation of the hypothesis that AA may derive a greater benefit from sipuleucel-T. The product parameters and AE profiles for AA are similar to that of the general population studied.