Background: Darolutamide (DARO) is a structurally distinct and highly potent androgen receptor inhibitor. In the phase 3 ARASENS study (NCT02799602) in patients (pts) with metastatic hormone-sensitive prostate cancer (mHSPC), DARO + ADT + docetaxel significantly reduced the risk of death by 32.5% vs ADT + docetaxel (hazard ratio 0.68; 95% confidence interval 0.57–0.80), with a favorable tolerability and safety profile. In the global (excluding US), phase 3 ARANOTE study (NCT04736199), DARO + ADT vs ADT alone is being evaluated in pts with mHSPC. ARASEC (NCT05059236) will complement ARANOTE by assessing DARO + ADT in US pts. As ADT alone is no longer an acceptable comparator in the US, the external control arm will be derived from the historical US CHAARTED study (NCT00309985). A real-world analysis of electronic health record data from pts with mHSPC (TIMES) indicated that there was minimal risk of historical time bias associated with the use of the external ADT alone arm from CHAARTED as a comparator for ARASEC (Shore N, et al. J Clin Oncol 2022;40(28 Suppl):Abstract 403). Methods: ARASEC is a phase 2, open-label, single-arm study enrolling pts with confirmed mHSPC and no prior systemic therapy. Pts will receive DARO 600 mg orally twice daily + ADT (luteinizing hormone-releasing hormone agonist/antagonist or orchiectomy). The external control arm will be derived from 394 pts with mHSPC treated with ADT alone in CHAARTED. To remove biases in evaluating outcomes that could arise due to differences in baseline profiles between arms, pts will be matched 1:1 using a propensity score (PS) summarizing baseline characteristics relevant to disease outcomes. Baseline variables will include age ( < 70 vs ≥70 years), Eastern Cooperative Oncology Group performance status (0–1 vs 2), CHAARTED-defined extent of disease (low vs high volume + bone metastases only vs high volume + visceral metastases ± bone metastases), and prior therapy (yes vs no; as a proxy for recurrent vs de novo disease). Matching patients with scores within a narrow window across the cohorts will ensure that pts in CHAARTED are representative of pts in the DARO + ADT arm. The primary endpoint is progression-free survival (PFS), as defined in CHAARTED. Secondary endpoints include overall survival, radiographic PFS, time to CRPC, undetectable prostate-specific antigen response rate ( < 0.2 ng/mL) at 6 months, and safety. Target enrollment for the DARO + ADT arm is 200 pts at 30 sites. The study will continue until either the event count threshold triggering the primary endpoint analysis has been met (161 PFS events) or all pts have been followed for ≥2 years, whichever occurs later. As of January 2023, 121 pts have been enrolled. A per-protocol, predefined matching exercise on the first 100 pts enrolled will be conducted to ensure that the planned sample size is adequate. Clinical trial information: NCT05059236.