Background: The most common therapy FL pts receive remains chemotherapy which yields high efficacy but also significant toxicity.(Marcus 2017, Rummel 2013). FL pts are largely aged over 65 and may require treatment multiple times over their disease course thus novel regimens which enhance efficacy and minimise toxicity are highly desirable. FL patient (pt) outcomes are influenced by tumor microenvironment composition and manipulation with immunotherapy. Ikaros and Aiolos, key cell development and homeostasis transcription factors are upregulated in FL. Cereblon-modulating compounds (CELMoDs) such as golcadomide (G) promote degradation of these with demonstrated efficacy alone or with rituximab (R) in FL (responses-ORR- upto 75% in heavily pre-treated FL pts) (Morschhauser 2018, Michot 2021). We reported favourable efficacy of nivolumab (N) a PD1 inhibitor plus R in 1L treatment of FL (ORR 92% complete response CR 54%). (Hawkes 2021).This study (‘TOP-FLOR’; NCT05788081) builds on these findings and potential immunomodulatory synergy to explore the efficacy and safety of R + G, a novel CELMoD +/- N in treatment-naïve advanced stage FL pts. Methods: This is an open label multicentre umbrella Bayesian Optimal randomised Phase 2 trial (n=40). Eligibility includes: age >18 years, treatment-naïve, stage II-IV, low grade FL, ECOG 0-2. Pts from 5 Australian sites are randomised 1:1 to receive 8 cycles of R-G +/-N 8 cycles of 28 days (D) each as follows: Arm A; R 375 mg/m2 IV D1 + G 0.4 mg orally D1- 14; Arm B; R-G as above +N 480mg IV D1. All pts in partial response (PR) or CR post cycle 8 receive 8 doses of 12-weekly R maintenance. The primary endpoint (EP) is CR rate post induction in the absence of prohibitive toxicity (CTCAE V5.0). Secondary EP are overall toxicity, ORR (as per Lugano criteria), time to treatment failure, progression free survival, overall survival. Exploratory EP include: pt reported outcomes, PET radiomics, laboratory biomarkers. Study assessments include safety assessments every cycle until D28 post final study drug delivery. Response assessments (PET/CT), pt reported outcomes & biomarker bloods are performed at baseline, post cycles 2, 5 & 8, then 6 monthly during R maintenance. Futility analysis occurs after 11 pts are recruited to each arm with < 7 pts achieve the primary EP. Treatment arms will not be formally compared. Kaplan-Meier analysis will be used to report survival probabilities. This trial received IRB approval on 14 July 2023 (HREC/88597/Austin-2023). To date 15 pts have been randomised. Clinical trial information: NCT05788081.