Here is the design of a clinical trial:

Official Title: Randomized Phase II Study Comparing Neo-epitope Based Vaccine OSE2101 (TEDOPI®) With or Without Anti-PD1 (Pembrolizumab) Versus Best Supportive Care as Maintenance Treatment in Platinum-sensitive Recurrent Ovarian Cancer Patient With Controlled Disease After Platinum-based Chemotherapy

Included conditions:
- Platinum-sensitive Ovarian Cancer
- Relapsed Ovarian Cancer

Study Armgroups:
- {'label': 'Arm A : Best Supportive Care', 'type': 'NO_INTERVENTION', 'description': 'Observational arm (Standard of care)'}
- {'label': 'Arm B : OSE2101', 'type': 'EXPERIMENTAL', 'description': 'OSE2101 monotherapy - subcutaneous injection on day 1, every 3 weeks for 7 doses then every 6 weeks up to week 48 and then every 12 weeks until intolerance, disease progression, or up to 2 years.\n\nOSE2101 vaccine is an emulsion of peptides suspension in in Montanide® ISA 51 adjuvant and containing 0.5 mg/mL of each 10 synthetically manufactured peptides (5.0 mg/mL total peptide) in 1.5 mL of emulsion.', 'interventionNames': ['Drug: OSE2101']}
- {'label': 'Arm C : OSE2101 + Pembrolizumab', 'type': 'EXPERIMENTAL', 'description': 'OSE2101 (subcutaneous injection on day 1, every 3 weeks for 7 doses then every 6 weeks up to week 48 and then every 12 weeks until intolerance, disease progression, or up to 2 years) + pembrolizumab (400 mg IV infusion on day 1 every 6 weeks until intolerance, disease progression, or up to 2 years.', 'interventionNames': ['Drug: OSE2101', 'Drug: Pembrolizumab 25 MG/ML [Keytruda]']}

Interventions:
- {'type': 'DRUG', 'name': 'OSE2101', 'description': 'subcutaneous injection on day 1, every 3 weeks for 7 doses then every 6 weeks up to week 48 and then every 12 weeks until intolerance, disease progression, or up to 2 years.', 'armGroupLabels': ['Arm B : OSE2101', 'Arm C : OSE2101 + Pembrolizumab'], 'otherNames': ['TEDOPI®']}
- {'type': 'DRUG', 'name': 'Pembrolizumab 25 MG/ML [Keytruda]', 'description': '400 mg IV infusion on day 1 every 6 weeks until intolerance, disease progression, or up to 2 years.', 'armGroupLabels': ['Arm C : OSE2101 + Pembrolizumab'], 'otherNames': ['KEYTRUDA®', 'MK-3475']}

Primary Outcomes:
- {'measure': 'Progression free survival (PFS)', 'description': 'Progression-free survival (PFS) is the time from randomization to progression measured radiologically using RECIST v1.1 guidelines as reported by the investigator or death, whatever the cause, whichever comes first. Patients alive and free of progression at the cut-off date will be censored at the last tumor assessment date', 'timeFrame': 'from date to randomization to date of event, assessed up to 4 years'}

Please estimate the sample size based on the assumption: 
The trial is designed with a type I error rate (α) of 5% and a type II error rate (β) of 10%, with one-sided tests. The sample size calculation ensures 90% power to detect the improvement in PFS. Hierarchical testing will be employed using one-sided log-rank tests with a nominal α value of 0.05. The trial assumes a 2-year accrual period and a minimum 1-year follow-up per patient.
3.7.
        Statistical methods & sample size determination
        This proof-of-concept trial aims to assess the efficacy of two investigational treatments (Arms B and C) compared with best supportive care (Arm A) as the control group. The primary end point isÂ PFS, measured from randomization to disease progression. Sample size calculations were conducted using SAS 9.4 power analysis software.
        The trial is designed with a type I error rate (Î±) of 5% and a type II error rate (Î²) of 10%, with one-sided tests. Previous trials have shown short median PFS in patients with platinum-sensitive relapse who responded to re-challenge with platinum doublet: 5.5Â months for BRCA-mutated patients and less than 4Â months for non-BRCA-mutated patients. We anticipate a slightly shorter PFS (<4Â months) in our population, as most patients will have received a PARP inhibitor and are required to have non-progression on platinum chemotherapy rather than an objective response per RECIST criteria. The combination of OSE2101 and pembrolizumab is hypothesized to outperform both OSE2101 alone and best supportive care (BSC). If the combination does not outperform BSC, no difference is expected between OSE2101 alone and BSC.
        Hierarchical testing (fixed sequence procedure) will be employed to compare the treatment arms, using three one-sided log-rank tests in a predefined order:1.**H1**: Arm C (OSE2101Â +Â pembrolizumab) vsÂ Arm A (BSC)- If H1 is statistically significant, proceed to:2.**H2**: Arm C (OSE2101Â +Â pembrolizumab) vsÂ Arm B (OSE2101)- If both H1 and H2 are statistically significant, proceed to:3.**H3**: Arm B (OSE2101) vsÂ Arm A (BSC)

        All one-sided tests in this sequence will use a nominal Î± value of 0.05. If H1 is not rejected, further tests will be exploratory.
        The sample size is calculated to ensure 90% power to detect an improvement in PFS for the combination therapy compared with BSC, with a hazard ratio (HR) of 0.57 (assuming median PFS increases from 4 to 7Â months under the exponential distribution of PFS), and an imbalanced randomization of 2:1. This design requires 121 events (progression or deaths) to test H1. Assuming a 2-year accrual period and a minimum 1-year follow-up per patient, 180 patients need to be randomized across Arm A (nÂ =Â 45), Arm B (nÂ =Â 45)Â and Arm C (nÂ =Â 90) to observe the required events.
        With 45 patients in the OSE2101 monotherapy arm, the trial will have 78% power to detect an HR of 0.57 compared with the BSC arm.