Main Menu


PERSEUS1: A phase II trial of the Immune Checkpoint Inhibitor Pembrolizumab for Patients Suffering from Metastatic Prostate Cancer.

Disease site: Prostate cancer

Treatment modality: Systemic therapy

Status: Open

Trial details

PERSEUS1 is a phase II, open-label, single arm, multicentre trial to determine the efficacy of pembrolizumab in patients with metastatic castration resistant prostate cancer (mCRPC) with high mutational load (HIMUT) or a DNA repair defect including mismatch repair deficiency (MMR-) after progression on standard treatments.

The trial involves two parts; Part A and Part B.

Part A will recruit 45 patients in stages. Initially 24 participants will be entered into the trial at stage 1. If more than 5 responses are reported in this stage, the trial will proceed to stage 2 where a further 21 participants will be enrolled.

Part B is the biomarker enrichment stage and will focus on stratified recruitment into biomarker defined cohorts in order to increase the precision with which the response rate can be estimated within mCRPC molecular subgroups of interest. It is anticipated that approximately 55 participants will be enrolled in Part B of the study, to make a total of 100 mCRPC participants in parts A and B over a period of 24 months from multiple UK sites.

Patients will receive pembrolizumab for up to 2 years. Patients who discontinue treatment without showing disease progression on imaging scans will enter safety follow-up (short term follow up period) and will be followed up for radiological disease progression every 12 weeks until:

1) 2 years after the last dose of pembrolizumab; 2) start of a new antineoplastic therapy;

3) documented disease progression, or 4) until death, whichever occurs first.

Patients with disease progression will be followed up for survival status.

Tumour responses will be defined on the following outcomes measured at 6 months post-trial entry:

  • Objective response by iRECIST 1.1
  • PSA decline of ≥50%
  • CTC count conversion from >5 to <5

Further information

Chief Investigator: Professor Johann de Bono, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust.

ICR-CTSU Scientific Lead: Professor Emma Hall

Trial management contact: [email protected] ID: NCT03506997

Sponsor: The Institute of Cancer Research

Funding: Merck Sharp and Dohme (MSD)

Further information including recruitment progress is available from: UK Clinical Trials Gateway

Publications and presentations

There have been no presentations or publications to date.

Clinical trials

Division of Clinical Studies

The division carries out or coordinates high-quality trials and translational research at both an early phase – typically to test new targeted drugs – and a later stage.