A pilot study of the liposomal MUC1 vaccine BLP25 in prostate specific antigen failures after radical prostatectomy

Purpose: Men with biochemical failure after radical prostatectomy have few therapeutic options other than androgen deprivation therapy. Targeted therapies in this group are appropriate because the optimal timing of the initiation of hormonal therapy in this patient population is unknown. A single institution pilot trial was performed using BLP25 liposome vaccine in hormone naive patients with prostate specific antigen failure after radical prostatectomy to determine if prostate specific antigen progression could be halted. Materials and Methods: Men with biochemical failure after radical prostatectomy were enrolled. Primary end points were efficacy and safety of the MUC1 BLP25 liposomal vaccine. Changes in prostate specific antigen doubling time were also evaluated. Patients received a single intravenous dose of cyclophosphamide, followed by vaccinations with BLP25 liposome vaccine for up to I year. Prostate specific antigen was measured at baseline and during treatment, and prostate specific antigen doubling time was calculated for these intervals. Results: A total of 16 patients with a median age of 60 years were enrolled. All patients received cyclophosphamide and 15 of 16 completed the primary treatment period. Ten patients completed the maintenance period. After the 8-week primary treatment period 8 of 16 patients had stable or decreased prostate specific antigen. At the last on-study prostate specific antigen measurement 1 patient maintained stable prostate specific antigen but all others had progression. However, 6 of the 16 patients had greater than 50% prolongation of prostate specific antigen doubling time compared to pre-study prostate specific antigen doubling time. Conclusions: BLP25 liposome vaccine shows promise for prolonging prostate specific antigen doubling time in hormone naive men with biochemical failure after prostatectomy and little morbidity. This could potentially translate into the deferral of hormonal therapy. Further testing in this population of patients is warranted.