CYCLONE 2: A phase 3 study of abemaciclib with abiraterone in patients with metastatic castration-resistant prostate cancer.
Authors: Smith Matthew Raymond , Piulats Josep M. , Todenhöfer Tilman , Lee Jae-Lyun , Arranz Arija Jose Angel , Mazilu Laura , Azad Arun , Alonso-Gordoa Teresa , McGovern Ursula Brigid , Choudhury Atish Dipankar , Ye Dingwei , Suzuki Hiroyoshi , McKay Rana R. , Ades Steven , Flechon Aude , Pieczonka Christopher Michael , Hulstijn Maarten , Lithio Andrew , Nacerddine Karim , Agarwal Neeraj 
Published: June 2024

5001 Background: Oncogenic addiction to androgen receptor (AR) signaling drives mCRPC progression, highlighting the unmet need for novel treatment strategies to maximize AR-directed therapy. Preclinical evidence suggests a key role for CDK4/6 in sustained AR signaling, uncontrolled proliferation, and hormonal resistance in prostate cancer. Abemaciclib (ABEMA) is a potent CDK4/6 oral inhibitor that significantly augments the efficacy of endocrine therapy in hormonally driven (ER+) high-risk early-stage and metastatic breast cancer. ABEMA also showed single-agent activity in heavily pretreated mCRPC. Here, we report the primary results of CYCLONE 2, a Phase 3 study of ABEMA plus abiraterone (ABI) in pts with 1L mCRPC. Methods: CYCLONE 2 was a seamless Phase 2/3 adaptive trial with a dose-finding safety lead-in. Randomization to the ABEMA or placebo (PBO) plus ABI and predniso(lo)ne was stratified by prior docetaxel receipt for mHSPC, measurable disease, and radiographic progression at study entry. Primary endpoint was investigator-assessed radiographic progression-free survival (rPFS) per RECIST v1.1 and PCWG3. The study was powered at ~90%, assuming a HR of 0.55 for rPFS, at a cumulative 2-sided alpha level of 0.05. Results: Between Nov 2018 and Jul 2022, 393 pts were randomized. Baseline characteristics were balanced across arms. Primary endpoint of rPFS was not met (HR 0.829; 95% CI, 0.619–1.111; p=0.2123), medians were 21.96 months for the ABEMA plus ABI group vs 20.28 months for the PBO plus ABI group. rPFS by blinded independent central review was consistent with investigator assessment (HR 0.842; 95% CI, 0.611–1.160). OS was a gated secondary endpoint and not inferentially tested (HR 0.927; 95% CI, 0.669–1.285; 38.9% maturity). Other secondary endpoints included time to PSA progression (HR 0.637; 95% CI, 0.474–0.856), time to symptomatic progression (HR 0.768; 95% CI, 0.522–1.131), and time to worst pain progression (HR 0.935; 95% CI 0.665–1.314). The most common grade ≥3 adverse events (AEs) reported in the ABEMA plus ABI group were anemia (13.6% vs 4.3% in the PBO plus ABI group), neutropenia (12.6% vs 0.5%) and ALT increased (8.7% vs 6.5%). Discontinuations of all study treatments due to AEs were 13.1% vs 4.3% in ABEMA plus ABI vs PBO plus ABI groups, while discontinuations of ABEMA or PBO alone due to AEs were 5.8% vs 1.6%, respectively. Conclusions: In patients with mCRPC, adding abemaciclib to abiraterone did not significantly increase rPFS. While no OS detriment was observed, secondary endpoints were not meaningfully improved. Overall, the combination was well tolerated, and safety was consistent with the known profiles of the individual medicines. Clinical trial information: NCT03706365 Clinical trial information: NCT03706365 .