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.
Pathologically confirmed rectal adenocarcinoma.
Neoadjuvant therapy based on radiotherapy; post-radiotherapy evaluation ≥8 weeks later shows near clinical complete response (near-cCR) or partial response (PR) with residual tumor <2 cm.
Tumor distance from the anal verge ≤5 cm.
Age 18-75 years.
Age <18 or >75 years.
Concurrent or previous malignancy within the past 5 years (except adequately treated basal-cell or squamous-cell skin carcinoma or carcinoma in situ of the cervix).
Emergency surgery required for bowel obstruction, perforation, or bleeding.
Prior colorectal surgery that may compromise intestinal reconstruction.
Single group
Selective Total Mesorectal Excision Based on Intra-Operative Frozen Section From Local Excision
Procedure/SurgeryAll participants undergo trans-anal full-thickness local excision under general anesthesia. The specimen is sent for intra-operative frozen-section pathology. 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.
2-year local recurrence rate
2-year local recurrence rate: defined as any clinical, radiologic, or pathologic evidence of tumor regrowth within the pelvis detected by digital rectal examination, endoscopy, CT/MR or PET-CT imaging, and biopsy (if indicated).
Rate of major surgical complications within 30 days post operation
Surgical complications graded ≥ III by the Clavien-Dindo classification (III = requiring surgical, endoscopic or radiologic intervention; IV = life-threatening complication requiring IC/ICU admission; V = death attributable to the complication).
Rate of permanent stoma at 2 years
Participants alive at 24 months who still have an end-colostomy or ileostomy deemed permanent by the treating surgeon.
Rate of anal incontinence at 2 years
Wexner score \> 10 points assessed by validated questionnaire.
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