Sipuleucel-T (Provenge®) for castration-resistant prostate cancer.

UNLABELLED: Sipuleucel-T is known to be very well tolerated and to prolong overall survival, but not progression-free survival, measured according to prostate-specific antigen variations and radiographic progression. Its exact mechanism is unknown. Although the article does not present new data, a new way of assessing immunotherapy efficacy is proposed. This involves measuring 'consecutive' times to progression, in an attempt to capture the delayed effects of immunotherapy.
OBJECTIVE: To propose a new way of assessing immunotherapy efficacy. Since 2010, the therapeutic armamentarium for prostate cancer has expanded to include the potent taxane agent cabazitaxel, the CYP17A1 inhibitor abiraterone and the novel immunotherapy agent sipuleucel-T (Provenge®. Demdreon, Seattle, WA, USA). Sipuleucel-T is an antigen-specific active immunotherapy agent, which is not designed to be directly toxic to tumour cells, but to help the immune system to selectively attack cancerous cells. We aimed to provide a comprehensive review of available safety and efficacy data about Sipuleucel-T.
METHODS: A systematic analysis of the literature was conducted using the terms 'Sipuleucel-T' and 'Provenge'. PUBMED was the main search engine, but abstracts published by the American Society of Clinical Oncology and the European Society of Medical Oncology, as well as press releases and product monographs, were also considered for inclusion. Reference lists of key articles were searched for further leads. Articles providing safety and efficacy data were included in this review.
RESULTS: Sipuleucel-T is based on autologous dendritic cells, which are collected by leukapheresis of peripheral blood, co-cultured with a modified PAP protein, and then re-injected intravenously. It is the first agent of its kind to obtain Food and Drug Administration approval for any kind of malignant tumour. Its approval was determined by the results of a placebocontrolled, randomized trial (the IMPACT trial), conducted in 512 asymptomatic or minimally symptomatic mean with metastatic castration-resistant prostate cancer. Although no difference in time to progression or PSA response rate was reported, a statistically meaningful 4.1-month improvement in median survival was achieved in the active arm with respect to the placebo arm (25.8 months vs 21.7 months). After Food and Drug Administration approval in April 2010, in view of the high economic cost of sipuleucel-T and the not completely flawless study design of the IMPACT trial, a national coverage analysis of sipuleucel-T was conducted by the Centers for Medicare and Medicaid Services. Such analysis has recently concluded that sipuleucel-T is a 'necessary and reasonable' treatment.
CONCLUSION: Sipuleucel-T is an effective treatment for prostate cancer, although its widespread use is uncertain for complex social and economic reasons.