Stereotactic ablative radiotherapy combined with fruquintinib and tislelizumab in metastatic colorectal cancer: Updated findings from a single-arm, prospective phase II trial (RIFLE).

e15570 Background: Stereotactic ablative radiotherapy (SABR) has been shown to sensitize immunotherapy through inducing immunogenic death and remodeling the tumor immune microenvironment. In addition, anti-angiogenic therapy exhibits synergistic antitumor effects with PD-1/PD-L1 antibodies through its immunomodulatory effects for metastatic colorectal cancer (mCRC) patients. Here, we report the updated results from RIFLE trial: the efficacy and safety of the combination of fruquintinib, PD-1 inhibitor tislelizumab and SABR in mCRC patients. Methods: This is a single-center, single-arm, prospective phase II clinical trial (NCT04948034). mCRC patients with at least 2 measurable lesions (≥1 of which can be targeted with radiation and ≥1 lesion outside the radiation field) who have failed ≥ 1L standard therapy will receive SABR followed by fruquintinib (5 mg, d1-14, qd) and tislelizumab (200 mg, d1, q3w) within two weeks from completion of radiation. The percentage change from baseline in the sum of longest diameter of target lesions, consist of specified radiated and non-radiated lesions, will be assessed after at least 2 cycles’ drug treatment. Primary endpoint is best objective response rate (ORR) of target lesions. Secondary endpoints include disease control rate (DCR), duration of response (DoR), progression-free survival (PFS) rate, overall survival (OS) rate and toxicity. Results: From August 2021 to February 2024, 34 patients were included in the trial and 31 in the efficacy analysis. Median age was 62 years, 24 (77.4%) patients were male, 26 (83.9%) had ≥ 3 metastases, and 14 (45.2%) had received ≥ 3 prior lines of systemic therapy. The biological effective dose (BED) for irradiated lesions ranged from 37.5 to 105 Gy. Median study follow-up was 17.3 months (95%CI:13.841-20.759), 24 patients were alive and 13 remained on treatment. 1 patient achieved complete response (CR) for target lesions, 8 partial response (PR), 14 stable disease (SD), illustrating an ORR of 29% and a DCR of 74.2%. Median PFS was 8.8 months (95%CI:5.868-11.732). The most common treatment-related adverse events (TRAEs) were proteinuria (35.5%), hypertension (22.6%) and rash (19.4%). Grade 3-4 AEs occurred in 9 patients, including proteinuria and hypertension, and there were no treatment-related deaths. Conclusions: SABR combined with tislelizumab and fruquintinib shows promising effects and good safety in the treatment of metastatic colorectal cancer, which is expected to provide new therapeutic strategies and improve the prognosis for mCRC patients. Clinical trial information: NCT04948034 . [Table: see text]