Selective Total Mesorectal Excision Based on Intra-Operative Frozen Section From Local Excision in Rectal Cancer Undergoing Neoadjuvant Chemoradiotherapy

This study is a prospective, single-arm, phase II superiority trial to determine whether a selective organ-preserving strategy based on immediate intra-operative frozen-section results can achieve favorable 2-year local control while lowering morbidity in patients with low rectal cancer (tumor ≤5 cm from the anus) who have a near clinical complete response (near-cCR) or partial response (residual tumor \<2 cm) after radiation therapy. Population: Adults with primary rectal adenocarcinoma located ≤5 cm from the anal verge who, after neoadjuvant radiotherapy, are judged to have near-cCR or partial response (residual tumor \<2 cm). Intervention: All participants undergo local excision under general anesthesia. The specimen is sent for intra-operative frozen section. ypT0-1 on frozen section → procedure concluded; patient enters watch-and-wait. ypT2-3 or R1 on frozen section → immediate completion total mesorectal excision (TME). Frozen-section ypT1-2 but final paraffin section up-staged to ypT2-3 or R1 → elective TME within 8 weeks. Primary Endpoint: a composite outcome of 2-year local recurrence rate, surgical complications (≤30 days), and long-term functional impairment (anorectal, urogenital, and quality-of-life scales). Secondary Endpoints: Agreement between intra-operative frozen-section pathology and final paraffin-section pathology, 3-year disease-free survival (DFS), 3-year overall survival (OS), surgery-sparing rate, post-operative recovery metrics, Quality-of-life scores. Estimated Enrollment: 27 participants.