THE CLINICAL ROLE OF PEPTIDE VACCINES FOR CASTRATION-RESISTANT PROSTATE CANCER

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Abstract

Introduction

Androgen deprivation therapy (ADT) is the standard treatment of metastatic prostate cancer. Although ADT achieves disease stabilization in the beginning of the treatment, most patients eventually develop castration-resistant prostate cancer (CRPC). Docetaxel (DTX)-based chemotherapy has been proved the efficacy for CRPC, however, the prognosis of patients after the induction of chemotherapy is limited. Therefore, extending the period from the diagnosis of CRPC to the induction of chemotherapy may contribute to improvement of overall survival of those patients. Immunotherapy is being developed for several malignancies including prostate cancer. We have previously carried out phase-I/II study of personalized peptide vaccination in metastatic CRPC patients, and showed the safety and effectiveness of peptide vaccination therapy. Since cancer immunotherapy may act more effectively in early stage of the disease before systemic chemotherapy, we conducted a randomized phase II study to evaluate the efficacy of the peptide vaccination therapy for chemotherapy-naïve CRPC patients.

Patients and methods

The patients are randomly assigned to two groups; one (vaccination group) receives the combination therapy of peptide vaccines and low-dose (1 mg/day) dexamethasone (Dx) and the other receives Dx alone. In the vaccination group, maximum of four kinds of peptide from those that have been recognized by the patient-specific immune system (serum IgG antibodies) in the peripheral blood are selected as vaccines. 3mg of each peptide is administrated separately every 2 weeks. Dexamethasone 1 mg/day p.o. is started on the first day of peptide administration. The primary end point of the study is progression-free survival and secondary end points include objective response rate and subjective effects.

Results

Up to now, 72 CRPC patients were enrolled in this study and 60 were evaluable and analyzed in detail. Median age was 68 years old (48–80 years) and median serum PSA was 4.8 ng/ml. The patients in vaccination group showed a significantly longer PSA progression free survival (P < 0.05). The preliminary results will be presented.

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