First in human intraarterial delivery of tislelizumab for the treatment of pMMR locally advanced rectal cancer: A single-arm, open label, phase II clinical trial

Background: Intravenous immune checkpoint inhibitors (ICIs) have shown efficacy in treating locally advanced rectal cancer (LARC), but concerns about systemic toxicity persist. This study developed a unique approach termed chemo-immuno-embolization with transcatheter rectal arterial intervention (CIETAI), aiming to enhance the anti-tumor response while minimizing systemic toxicity. Method: This is a prospective, single-arm, phase II clinical trial conducted in Daping hospital. Patients with previously untreated stage II/III LARC underwent preoperative CIETAI combined with PD-1 inhibitor tislelizumab plus oxaliplatin, followed by standard concomitant chemoradiotherapy (capecitabine and 50.4 Gy radiation). Intravenous tislelizumab was administered for an additional two cycles. Results: Between January 2023 and December 2023, a total of 38 patients were enrolled. As the primary endpoint, 17 (44.74 %) patients achieved pathological complete response (TRG0), with a major pathologic response (MPR) rate of 65.79 %. The anal preservation rate was 84.21 % (32/38), and importantly, 15 of 21 patients with low rectal cancer achieved organ preservation with functional maintenance. Eight patients experienced grade 3–4 adverse events (AEs). All immune-related AEs were grade 1–2, with the most common being endocrine toxicity (5/6, 83.33 %). No grade 5 AEs occurred. Conclusion: This study provides preliminary evidence supporting the safety and efficacy of intraarterial tislelizumab delivery in the neoadjuvant setting for LARC. These promising results encourage further exploration in larger cohorts to validate the clinical impact of this novel CIETAI strategy. Trial registration: ClinicalTrials.gov Identifier: NCT05957016.