RTID-03. A MULTICENTER, RANDOMIZED, CONTROLLED TRIAL OF FOCUSED-ULTRASOUND-MEDIATED BLOOD-BRAIN BARRIER DISRUPTION PLUS SYSTEMIC PEMBROLIZUMAB FOR PATIENTS WITH NSCLC BRAIN METASTASES (LIMITLESS)

Abstract BACKGROUND Systemic therapy for brain metastases (BM) is hindered by blood-brain barrier (BBB). Low-intensity focused ultrasound (LIFU), combined with IV microbubble oscillators, leads to non-invasive BBB disruption, which could enhance intracranial delivery of systemic immune checkpoint inhibitors. This randomized controlled trial (RCT) aims to evaluate safety and efficacy of LIFU-mediated BBB disruption plus systemic pembrolizumab for NSCLC BM. METHODS LIMITLESS (NCT05317858) is an ongoing, multicenter, parallel-arm, open-label RCT that randomizes NSCLC BM patients on standard-of-care pembrolizumab monotherapy to LIFU plus pembrolizumab (arm 1) or pembrolizumab alone (arm 2) in a 2:1 ratio. Included patients have age ≥18 years, normal organ function, KPS ≥70, EGFR- and ALK-negative primary tumor, and ≤3 BM with ≥1 BM meeting RANO-BM measurable disease criteria. All patients receive standard-of-care therapy, while those on arm 1 undergo LIFU before each pembrolizumab dose (200mg IV q3weeks). Patients undergo pre-treatment brain MRI, followed by IV microbubbles for enhanced sonication effects. MR-guided BBB disruption is performed using transcranial 220kHz LIFU device with real-time acoustic-feedback-based power control for maintaining effective microbubble activation. Pembrolizumab is infused immediately after sonication, and repeat MRI is done 24-48 hours later to assess treatment effects. Primary study outcome is overall objective response rate (ORR) at 6 months as assessed using RANO-BM. Using Bayesian design for power analysis, a superior ORR of 60% is assumed for LIFU arm versus 30% for control arm for total sample size of N=96 (64 participants in LIFU and 32 in control arm), for 80% power using two-sided chi-square test with alpha=0.05. For upper-bound estimate, ORR of 45% in LIFU arm and 30% in control arm, the study needs N=369 participants (246 in LIFU arm and 123 in control arm). Secondary outcomes are best ORR and median time-to-response. Exploratory outcomes are median progression-free survival (PFS), overall survival (OS), median intracranial PFS, median extracranial PFS, and quality of life. Patient enrollment commenced in 2022 and remains ongoing.