An Adaptive-design Prospective Cohort Study of Watch and Wait Strategy in Patients With Locally Advanced Rectal Cancer

• Primary objective:

Evaluate the CCR rate of low rectal cancer using adaptive and optimized chemotherapy and radiotherapy strategies (all population and dMMR/MSI-H subgroup)

• Secondary objectives:

2.1 Evaluate the 2-year anal preservation rate, recurrence rate, quality of life, DFS and OS 2.2 Explore the subgroup of patients suitable for observation.

• Outline:

Patients after long-course chemoradiation are grouped based on their MSI-H/dMMR status. For patients with MSI-H/dMMR, consolidation immunotherapy of Tislelizumab (BGB-A317) will be assigned. For patients with MSS/pMMR, consolidation chemotherapy will be given according to their tumor response. After completion of consolidation therapy, those who reach clinical complete response will receive organ preservation (watch and wait) strategy in place of radical surgery. During treatment, once local regrowth occurs or poor tumor response, total mesorectal excision (TME) surgery will be performed.

Inclusion criteria

• pathological confirmed adenocarcinoma
• clinical stage T2-4 and/or N+, inappropriate for local excision
• the distance from anal verge less than 5 cm, or considered inappropriate for anal preservation by surgeons.
• Strong desire to preserve the anus, able to receive close surveillance for at least 2 years after chemoradiotherapy.
• without distance metastases
• aged between 18 to 75 years old.
• performance status score: 0~1
• UGT1A1*28 6/6 or 6/7
• sign the inform consent

Exclusion criteria

• pregnancy or breast-feeding women
• serious medical illness
• difficult to achieve complete response assessed by current evidence: the maximal diameter of tumor >10cm; the maximal diameter of lateral lymph node >2cm; baseline CEA>=100; biopsy pathology confirmed signet ring cell carcinoma components; digital rectal examination found that the tumor is peri-narrowed.
• baseline blood and biochemical indicators do not meet the following criteria: neutrophils≥1.5×10^9/L, Hb≥90g/L, PLT≥100×10^9/L, ALT/AST ≤2.5 ULN, Cr≤ 1 ULN
• DPD deficiency
• UGT1A1*28 7/7