Node-Sparing Short-Course Radiation Combined With Capecitabine and PD-1/CTLA-4 for MSS Early Middle and Low Rectal Cancer (mRCAT-E): An Open-label, Single-arm, Prospective Multicenter Clinical Trial
This is a single-arm, prospective, multicenter study evaluating a novel neoadjuvant treatment strategy for patients with early, mid-low rectal adenocarcinoma that is microsatellite stable (MSS). Instead of irradiating regional lymph nodes, we deliver short-course radiotherapy (25 Gy in 5 fractions) exclusively to the primary tumor (lymph-node-sparing approach), immediately followed by four 3-week cycles of capecitabine plus combined PD-1/CTLA-4 immune checkpoint inhibitors. Two weeks after completing chemo-immunotherapy, tumor response is assessed. Patients who achieve a clinical complete response may enter a watch-and-wait program; others will undergo local excision or total mesorectal excision (TME) as appropriate. The primary endpoint is the rate of complete response (clinical and pathological). Secondary endpoints include organ-preservation rate, 3-year local recurrence, 3-year disease-free and overall survival, toxicity, and quality-of-life measures. Results from a pilot study suggest that this regimen may substantially improve complete response rates while reducing radiation-related toxicity, potentially allowing more patients to avoid radical surgery and permanent stoma.
• Patients who have a strong willingness to preserve the anus and are willing to receive neoadjuvant therapy.
• Male or Female aged 18-80.
• Patients diagnosed with low rectal cancer within 7 cm from the lower edge of the tumor to the anal verge by pelvic MRI and rectal ultrasound, the clinical stage is cT2-3N0M0.
• Histologically confirmed rectal adenocarcinoma; Genetic testing suggests MSI-L or MSS, or tumor biopsy immunohistochemistry reveals pMMR, that is, MSH1, MSH2, MSH6, and PMS2 are all positive.
• Eastern Cooperative Oncology Group (ECOG) score 0-1.
• No previous treatment (including anti-tumor therapy, immunotherapy or pelvic radiation).
• Informed consent form signed.