Background: Bleomycin, etoposide, and cisplatin (BEP) given 3-weekly x 4 remains standard 1st line chemotherapy for intermediate or poor risk metastatic GCT. Accelerating standard regimens by shortening the cycle length to 2-weekly improved cure rates in other cancers. P3BEP will determine effects of accelerated versus standard BEP in this setting. This is a first international, randomized trial of chemotherapy for intermediate and poor-risk metastatic GCT to include adults and children of both sexes.

Methods: This open label, randomized, phase 3 trial is conducted seamlessly in 2-stages. The primary endpoint for stage I (n=150) was complete response (CR); and for stage 2 (n=500) is progression free survival at 2 years (PFS2y). These sample sizes provide >80% power with a two-sided type I error rate of 5% to detect an absolute improvement of 25% in the CR rate (stage 1) and of 7% in the PFS2y (stage 2). The target population is males and females aged 11 to 45 with intermediate-or poor-risk metastatic GCT of the testis, ovary, retroperitoneum, or mediastinum. Participants are randomized (1:1) to 4 cycles of standard BEP (q3w) or accelerated-BEP (q2w) with cisplatin 20mg/m² D1-5, etoposide 100mg/m² D1-5, bleomycin 30 KIU weekly x 12, and pegylated G-CSF D6 or filgrastim daily. Study assessments occur at 30 days after completing chemotherapy, 6 months from randomization, and after completion of all post-chemotherapy treatments (e.g. surgery). Tumour and baseline blood samples are collected for translational substudies. Progress: As of Sept 2022, 226 participants have been recruited from 24 ANZ sites, 17 UK sites (led by Cambridge Clinical Trials Unit), and 149 USA sites (led by Children’s Oncology Group). The first planned interim analysis for safety (n=76) identified no safety concerns. Stage I analysis (n=150) showed sufficiently favorable results with no futility concerns, supporting ongoing trial recruitment.