Castration With Abiraterone 250 mg Without LHRH Analogs or Blockers in Patients With Prostate Cancer Requiring Hormonal Intensification (Multicenter Phase 2)

Design

* Type: Phase 2, prospective, open-label, multicenter, single-cohort. * Inclusion Criteria:

* Patients with standard indication for intensification:

* M0 high/very high risk candidates for RT (Abiraterone \[ABI\] for 2 years + ADT for 3 years per STAMPEDE), or * mHSPC: candidates for doublet (ADT+ABI) or triplet (ADT+Docetaxel+ABI); without ADT during the first 30 days.

Objectives and Endpoints

Primary:

1. Proportion of patients with serum testosterone ≤50 ng/dL (and sensitivity analysis ≤20 ng/dL) at Day 30 (±3) without receiving ADT. 2. Time to castration (first day with T ≤50 ng/dL within D1-D30).

Secondary:

* Absolute and % change in PSA between D0 and D30; PSA50 and PSA90 rates at D30. * Safety (CTCAE v5.0): hypertension, hypokalemia, hepatotoxicity, fluid retention, adrenal insufficiency.

Procedures and Timeline

* Screening (≤7 days): consent, medical history, ECOG, BP, ECG, labs: CBC, liver profile, creatinine, K+, PSA, testosterone. * Day 0: start ABI 250 mg + prednisone 5-10 mg/day; education on "with food" administration. * Day 30 (±3): AE, BP, K+, LFT, T, PSA → endpoint evaluation. * Safety follow-up: until Day 60.

Ethical and Regulatory Considerations

* In Argentina and Bolivia, time to access intensified treatment with Abiraterone (doublet or triplet) exceeds two months in the public system, so waiting time is not altered and patients may benefit from early intensified castration if trial is positive. * The 250 mg "with food" regimen has pharmacokinetic/economic support in literature; detailed in consent. Multiple studies confirm ABI 250 mg with food equals 1000 mg, and NCCN guidelines recommend this dosing in low-access settings. The SPARE study evaluated safety of ABI without ADT in metastatic castration-resistant prostate cancer, showing equivalence. * The 30-day window without LHRH is limited, and all patients will receive standard treatment.

Rescue and Safety Criteria • Key AE management:

* Hypokalemia: supplement; consider eplerenone (preferred over spironolactone for lower androgenic interaction); adjust steroid. * Hypertension: optimize antihypertensives. * Hepatotoxicity: pauses/adjustments per AAP guidelines.

Sample Size and Justification

* One-sample binomial test to reject p≤0.70 (unacceptable null) in favor of p≥0.90 (target). * With n=24 per cohort and success defined as ≥20/24 patients achieving castration at D30:

* α (one-sided) ≈ 0.042 if true p=0.70. * Power ≈ 0.91 if true p=0.90.

Variables and Analysis

* Primary: proportion with T ≤50 ng/dL at D30 (main analysis) and T ≤20 ng/dL (sensitivity).

o Estimate 95% CI and one-sided binomial test vs 70%. Cohort success if ≥20/24 meet criteria. * Secondary:

* PSA: absolute and % change, PSA50/PSA90 rates at D30. * Safety: AE rates (CTCAE v5.0).

Quality and Logistics

* Testosterone measurement (validated method; preferably LC-MS/MS) to avoid variability. * Written instructions for administration with food (same time, similar meal). * Home BP and AE recording (card/app).