Phase II Study of Ipilimumab in Men With Metastatic Prostate Cancer With an Incomplete Response to Androgen Deprivation Therapy

Abstract

Background: Phase 3 studies of immune checkpoint inhibitors have not shown a survival benefit in prostate cancer, but some patients have a profound anticancer response. Patients and Methods: We evaluated the efficacy of the CTLA-4 targeted agent, ipilimumab, in metastatic prostate cancer patients who had an incomplete biochemical response to initial androgen deprivation therapy (ADT) alone. Ten patients were enrolled, each treated with ipilimumab 10 mg/kg (every 3 weeks for up to 4 doses) with maintenance ipilimumab every 12 weeks for non-progressing patients. The primary endpoint was proportion of patients with an undetectable PSA. The total sample size was 30 patients, but there was an interim analysis planned at 10 for futility. If none of the 10 patients achieved an undetectable PSA, the study would be halted. Results: The study was halted at the interim analysis as none of the 10 patients achieved the primary endpoint, but 30% of patients demonstrated a >50% reduction in PSA, with one patient achieving a >90% reduction in PSA. Peripheral blood mononuclear cells (PBMC) examined by mass cytometry showed that patients with clinical responses had an increase in effector memory T-cell subsets as well as an increase in T-cell expression of T-bet, suggesting induction of a Th1 response. Conclusions: This study provides further evidence that ipilimumab has activity in some patients with prostate cancer and provides further rationale for the development of future studies aimed at identifying a subset of patients with CPRC that are more likely to derive a benefit from treatment with ipilimumab. Implications for Practice: There is insufficient evidence to use ipilimumab in prostate cancer in routine practice. Trial Registration: ClinicalTrials.gov, NCT01498978. Registered 26 December 2011. https://www.clinicaltrials.gov/ct2/show/NCT01498978?term=julie+graff&rank=3.

Keywords: CTLA-4; checkpoint inhibitor; immunotherapy; metastatic; prostate cancer.

Copyright © 2020 Graff, Stein, Surana, Al Rabadi, Liu, Fong, Bailey, Latour, Newby, Moran and Beer.

Figures

Figure 1

(A) Best PSA response on study; (B) tumor and patient factors according to cancer response.

Figure 2

(A) PSA progression and time to next therapy; (B) overall survival.

Figure 3

Immune Characteristics. CyTOF assessment of peripheral blood mononuclear cells (PBMCs) from treated patients. (A) Pre-treatment PBMCs were compared to post-treatment PBMCs using Statistical Scaffold analysis. Landmark nodes are denoted in black and serve as reference points representing pre-determined cell subsets. Sample cluster sizes generated from distinct cell populations surround the landmark nodes and edges connect clusters to one another based on similarity to guide the development of Scaffold maps. Sample cluster sizes are scaled according to the population of each cluster. Clusters with statistically significant increase in the % of cells that are Ki-67 positive in post-treatment samples are denoted in red (q < 0.05). (B) Pre-treatment PBMCs in patients with PSA responses were compared to the PSA non-responders with Statistical Scaffold. Clusters with statistically significant increase in t-bet pre-treatment are denoted in red (q < 0.05). (C) Clusters with statistically significant increase in PD-1 pre-treatment are denoted in red (q < 0.05).