Scanning electron color-enhanced image depicts prostate cancer cells.
Photo courtesy Annie Cavanagh/Cell Image Library
Preliminary data suggest a promising role for sipuleucel-T as a treatment for African-American men with metastatic castration-resistant prostate cancer (mCRPC).
Colonel David G. McLeod, MD, chief of Urologic Oncology at Walter Reed Army Medical Center in Washington, DC, and coworkers elsewhere conducted a subgroup analysis in black patients enrolled in three phase III clinical trials of sipuleucel-T. The findings were released at the American Urological Association 2012 Annual Scientific Meeting held May 19-23 in Atlanta, Georgia.
Prostate cancer is more common in black men than white men. It has also been reported that the disease is biologically and genetically more aggressive in blacks, as evidenced by a more rapid growth rate and earlier transformation from latent to aggressive disease. Prostate cancer has been found to have a higher rate of metastatic spread (4:1) in African Americans versus Caucasians.
Sipuleucel-T is an autologous cellular immunotherapy that has been approved for the treatment of men with asymptomatic or minimally symptomatic mCRPC. The agent was designed to promote an immune response against prostatic acid phosphatase, an antigen expressed in the majority of prostate cancers.
Sipuleucel-T was approved for mCRPC on the basis of the phase III IMPACT study. At a median of 34 months of follow-up, sipuleucel-T 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 sipuleucel-T versus control group, respectively.
Of a total of 737 patients in the phase III studies, 488 were randomized to sipuleucel-T and 249 to placebo. Overall, 33 African-American patients were assigned to sipuleucel-T and 10 patients to placebo.
Results for the intent-to-treat population for the three studies demonstrated a positive treatment effect (HR = 0.735; 95% CI, 0.613-0.882; P
< .001). The difference in median OS was 3.9 months (25.4 months for sipuleucel-T and 21.5 months for placebo).
In the black population, men assigned to sipuleucel-T 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. Irrespective of race, a consistent survival benefit was observed in patients assigned to sipuleucel-T therapy versus patients assigned to placebo.
McLeod, professor of Surgery at the Uniformed Services University of the Health Sciences, Bethesda, Maryland, emphasized that the results are preliminary, given that the phase III studies enrolled only a small number of black patients. He noted that patients with advanced prostate cancer are currently being recruited into a multicenter registry of sipuleucel-T, which is expected to yield additional information on the role of sipuleucel-T in the treatment of black patients.
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.