Immunotherapy in metastatic prostate cancer

INTRODUCTION

Prostate cancer remains a challenge as a target for immunological approaches. The approval of the first cell-based immune therapy, Sipuleucel-T for prostate cancer introduced prostate cancer as a solid tumor with the potential to be influenced by the immune system.

METHODS

We reviewed articles on immunological management of prostate cancer and challenges that lie ahead for such strategies.

RESULTS

Treatments have focused on the identification of novel cell surface antigens thought to be unique to prostate cancer. These include vaccines against carbohydrate and blood group antigens, xenogeneic and naked DNA vaccines, and pox viruses used as prime-boost or checkpoint inhibitors. No single vaccine construct to date has resulted in a dramatic antitumor effect. The checkpoint inhibitor, anti-CTLA-4 has resulted in several long-term remissions, but phase III trials have not demonstrated an antitumor effect or survival benefit.

CONCLUSIONS

Multiple clinical trials suggest that prostate cancer may not be optimally treated by single agent immune therapies and that combination with biologic agents, chemotherapies, or radiation may offer some enhancement of benefit.

Perspectives on sipuleucel-T: Its role in the prostate cancer treatment paradigm

Sipuleucel-T is an autologous cellular immunotherapy approved in the US for patients with asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). This significant advance for mCRPC treatment provides healthcare professionals with another effective therapy to extend survival. As an immunotherapy, sipuleucel-T possesses specific characteristics differentiating it from traditional therapies. At a roundtable meeting of experts, sipuleucel-T data were discussed, focusing on interpretation and clinical implications. Important differences between immunotherapies and traditional therapies were explored, e.g., mode of action, outcomes, data consistency and robustness, timing of sipuleucel-T treatment, and future perspectives in areas such as short-term markers of long-term benefit.

Targeted treatment of metastatic castration-resistant prostate cancer with sipuleucel-T immunotherapy

Context

Prostate cancer remains highly prevalent and has a poor clinical outcome once metastatic. Sipuleucel-T is an autologous cellular immunotherapy approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Sipuleucel-T treatment extends survival but is independent of traditional short-term markers of treatment response observed with chemotherapy and contemporary hormonal treatments. Therefore, it is essential that clinicians understand the mechanism of action of sipuleucel-T and how this can translate in the clinic.

Objective

This article aims to summarize the current knowledge of sipuleucel-T therapy and its effects in mCRPC.

Evidence acquisition

Relevant publications describing sipuleucel-T clinical data and information relating to immunotherapies were identified.

Evidence synthesis

Treatment with sipuleucel-T extends survival, with side effects being usually mild or moderate and manageable within the outpatient setting. The long-term immune responses generated by sipuleucel-T correlate with a survival benefit. Sipuleucel-T shows a greater magnitude of clinical benefit when used in patients earlier in the mCRPC setting.

Conclusions

Sipuleucel-T stimulates long-lived immune responses that translate into long-term clinical benefit. The treatment course (three infusions at weeks 0, 2, and 4) is associated with manageable side effects. Short-term markers of future benefit would be clinically useful, and information on effective treatment combinations or sequences is awaited.

Patient summary

Sipuleucel-T treatment directs the patient’s own immune system to target and remove prostate cancer cells and increases life expectancy. Patients whose cancer is less advanced generally have a more ‘active’ immune system and may benefit the most from this treatment.