Hu, Peng

Background: Conventional neoadjuvant chemoradiotherapy (nCRT) yields a pathologic complete response (pCR) rate of 15–30% for locally advanced rectal cancer (LARC). This study ventures to shift this paradigm by incorporating short-course nCRT with immunotherapy, specifically Envafolimab, to achieve improved treatment efficacy and possibly redefine the standard of care for LARC. Materials and methods: The PRECAM study is a prospective, single-arm, phase 2 clinical trial for LARC in patients with microsatellite stable (MSS) tumors. Participants received short-course radiotherapy (25Gy/5f), followed by two cycles of CAPEOX chemotherapy and six weekly doses of Envafolimab, a PD-L1 antibody, before total mesorectal excision surgery. The primary endpoint was the pCR rate. Results: From April to December 2022, 34 patients were enrolled, of whom 32 completed the study, each diagnosed with an MSS rectal adenocarcinoma. All patients underwent preoperative CRT combined with Envafolimab. Remarkably, a pCR rate of 62.5% (20/32) was attained, and a significant pathologic response rate of 75% (24/32) was achieved. Additionally, 21 of 32 participants achieved a neoadjuvant rectal (NAR) score below 8, suggesting an effective treatment response. Common adverse events included tenesmus (78.1%), diarrhea (62.5%), and leukocyte decrease (40.6%). Two Grade 3 adverse events were noted, one related to liver function abnormality and the other to a decrease in platelet count. Surgical procedures were performed in all cases, with minor complications, including ileus, infections, and anastomotic leakage. As of this report, there have been no reported cases of recurrence or death during the follow-up period, ranging from 12 to 20 months. Conclusion: In LARC patients exhibiting MSS tumors, combining short-course nCRT with Envafolimab demonstrated favorable efficacy, leading to a significant pCR rate. Minor adverse effects and surgical complications were observed. These preliminary but promising results underscore the potential of this approach and call for further exploration and validation through a randomized controlled trial.

3614 Background: Conventional neoadjuvant chemoradiotherapy (nCRT) yields a pathologic complete response (pCR) rate of about 15%–- 30% for locally advanced rectal cancer (LARC). This PRECAM study aimed to investigate the efficacy and safety of neoadjuvant short-course radiotherapy combined with CAPEOX plus Envafolimab in Patients with Microsatellite Stable (MSS) LARC, redefining the standard of care (SOC) for LARC. Methods: The study is an open-label, prospective, single-arm, phase II clinical study . Eligible patients with MSS LARC were consecutively enrolled. Participants received short-course radiotherapy (25Gy/5f) with subsequent two cycles of CAPEOX (capecitabine and oxaliplatin) and 6 cycles of Envafolimab (subcutaneous injection, 150 mg, QW ) followed by total mesorectal excision surgery. The primary endpoint was pathological complete response (pCR) rate, and the secondary endpoint was major pathologic (MPR) rate and safety. Results: From April to December 2022, 34 patients were enrolled, of whom 32 completed the study. Remarkably, The pCR rate was62.5% (20/32), and the (MPR) rate was 75% (24/32). Furthermore, 65.6% (21/32) patients achieved a neoadjuvant rectal (NAR) score below 8, suggesting an effective treatment response. Common adverse events included tenesmus (78.1%), diarrhea (62.5%), and leukocyte decrease (40.6%), with two cases of Grade 3 adverse events. Surgical procedures were performed in all 32 cases, with minor complications observed. During the follow-up period of up to 20 months, no recurrence or death were reported. Conclusions: Short-course radiotherapy combined with CAPEOX plus Envafolimab showed favorable pCR rate with manageable adverse effects and surgical complications in LARC, underscoring the potential of the combination therapy for MSS LARC. A Randomized controlled trial is warranted for further exploration and validation. Clinical trial information: NCT05216653 .