Combination of PD-1 blockade and neoadjuvant chemoradiotherapy benefits pMMR/MSS patients with locally advance rectal cancer: A phase 2 clinical trial.

For patients with mismatch repair-proficient / microsatellite stable (pMMR/MSS) locally advanced rectal cancer (LARC), the NECTAR (NEoadjuvant Chemoradiotherapy plus immunoTherapy for locally Advanced Rectal cancer) trial reported an encouraging pathological complete response (pCR) rate of 40.0%. Given that pMMR/MSS tumors are generally resistant to immunotherapy, this pCR rate highlights the potential of combination therapy to overcome primary resistance. Here, we report the 3-year survival outcomes of the NECTAR trial, using neoadjuvant chemoradiotherapy (NCRT) plus tislelizumab in pMMR/MSS LARC. In this phase 2, multi-center, single-arm trial, eligible pMMR/MSS LARC patients received three cycles of neoadjuvant programmed cell death protein 1 (PD-1) blockade, three cycles of chemotherapy, and long-course radiotherapy followed by total mesorectal excision (TME). This 3-year analysis evaluates disease-free survival (DFS) and safety. From June 2021 to November 2022, 50 patients were enrolled and 46 patients completed neoadjuvant therapy and TME. Of the 46 patients, 20 patients reached pCR. With a median follow-up of 44.2 months, the median DFS was not reached. The 3-year DFS rate was 89.1%. All patients who achieved pCR (20/46) remained DFS at 3 years. Patients with a low neoadjuvant rectal (NAR) score (<8) had the 3-year DFS rate of 100%, suggesting that overcoming therapeutic resistance in immunotherapy may translate into sustained survival benefits. No new grade ≥III treatment-related adverse events (trAEs) occurred during the 3-year follow-up. The 3-year survival outcomes demonstrate promising efficacy and safety of this NECTAR trial, which provides a promising therapeutic avenue for a patient population traditionally resistant to single-agent immunotherapy.