Biomira Inc. has announced publication of study results showing that Stimuvax, formerly known as BLP25 Liposome Vaccine or L-BLP25, could slow rising Prostate Specific Antigen (PSA) levels in some post-surgical prostate cancer patients, potentially delaying the need for initiation of androgen deprivation therapy (ADT).
The study results were described in an article entitled "A Pilot Study of the Liposomal MUC1 vaccine BLP25 in Prostate Specific Antigen Failures After Radical Prostatectomy" that appears in the July 2006 issue of the Journal of Urology. PSA is a tumour marker used by physicians to detect prostate cancer, monitor treatment effects and guide medical management of men with this disease, rising levels being predictive of relapse and disease progression.
The open-label phase 2 safety and efficacy trial, conducted at the Cross Cancer Institute in Edmonton, Alberta, enrolled 16 post-radical prostatectomy patients. Patients enrolled in the trial had undergone this surgery at least six months prior to study entry, but experienced rising PSA levels post-surgery, final measurements having increased at least 50 per cent above the lowest post-surgical level. The primary study endpoint was to determine if Stimuvax could stabilize or decrease serum PSA in these men; secondary endpoints included safety and immune response measurements. Study treatment consisted of a primary and maintenance phase.
The primary treatment phase included a single dose of cyclophosphamide, used as an immunomodulator to enhance the potential activity of Stimuvax, followed three days later by the first of eight weekly vaccinations. The maintenance phase followed, with the administration of vaccinations every six weeks for a maximum total of 15 doses over approximately one year.
While no decreases in PSA occurred during the study period, PSA stabilization occurred in 50 percent of patients at the end of the primary treatment phase, and was maintained in one patient at the end of the study. Another interesting outcome was a noted increase in the PSA doubling time, which was prolonged by more than 50 per cent in six men at the end of the trial, compared with the doubling time prior to vaccine treatment. These observations, along with favorable safety data, led the study's authors to conclude that immunotherapy with Stimuvax may "impart a positive effect on the population tested," warranting further testing in controlled studies in a larger patient population. Dr. Scott A. North, the study's principle investigator, said "Many men are placed on ADT, a therapy with significant side effects based on some pre-defined PSA level. Delaying the time to PSA level doubling may defer initiation of this treatment and spare patients the negative impact of the only therapy available to them for a longer period of time." He further commented that, "Since men with a longer PSA doubling time can expect longer survival than those with shorter times, a strategy to lengthen the time to doubling may favorably impact the disease."