This study investigates the feasibility of an organ-preserving "watch-and-wait" strategy in patients with mid-to-low rectal cancer who achieve a good response after total neoadjuvant therapy (TNT). By retrospectively and prospectively analyzing patients who complete TNT following effective induction chemotherapy, the study aims to assess organ preservation rates and evaluate whether non-surgical management can provide comparable oncologic outcomes to radical surgery while improving functional recovery and quality of life.

With the evolution of rectal cancer treatment concepts, achieving optimal oncologic outcomes while preserving organ function and improving patients' quality of life has become a major goal in the management of low rectal cancer. Multiple studies have reported that for patients who achieve a clinical complete response (cCR) after total neoadjuvant therapy (TNT), a watch-and-wait (organ preservation) strategy-with close follow-up and salvage surgery when necessary-yields 5-year disease-free survival (DFS) and overall survival (OS) rates comparable to those of patients who undergo radical surgery and achieve a pathological complete response (pCR). Moreover, compared with total mesorectal excision (TME), patients managed with a watch-and-wait approach demonstrate significantly better physical, cognitive, role, and social-emotional functioning, along with lower incidences of bowel, sexual, and urinary dysfunction.

This study aims to retrospectively and prospectively include patients with mid-to-low rectal cancer who respond well to induction chemotherapy and subsequently complete TNT, in order to observe the organ preservation rate after TNT and to preliminarily evaluate the feasibility of this treatment approach within a watch-and-wait strategy.

Inclusion Criteria:

• Age: 18-80 years; no restriction on sex.

• Histologically confirmed rectal adenocarcinoma with immunohistochemistry and/or genetic testing showing pMMR/MSS status.

• Tumor characteristics assessed by chest-abdominal CT, rectal ultrasound, and MRI meeting all of the following criteria:

  1. The lower edge of the tumor is ≤5 cm from the anal verge as measured by digital rectal examination or MRI;
  2. Clinical stage cT1-3abN0-1M0 (for cT1N0, patients suitable for endoscopic resection are excluded);
  3. MRF (-) (>1 mm), EMVI (±);
  4. Negative lateral lymph nodes and <7 mm in size;
  5. Maximum tumor length ≤5 cm;
  6. Tumor circumference involvement ≤2/3.

• After receiving at least two cycles of induction chemotherapy with the XELOX regimen, MRI assessment shows treatment response (tumor length reduced by ≥30% compared with baseline).

• Completion of total neoadjuvant therapy (TNT), including long-course chemoradiotherapy and consolidation chemotherapy (radiotherapy: 25-28 fractions; chemotherapy: 6-8 cycles).

• (For the prospective cohort) Provision of written informed consent for participation in this observational study.

Exclusion Criteria:

• Patients with a history of, or concurrent, other malignant tumors (except for cured basal cell carcinoma of the skin or carcinoma in situ of the cervix);
• Patients with severely incomplete clinical data that preclude effective evaluation;
• (For the prospective cohort) Patients who refuse to provide written informed consent.

Patients with mid-to-low rectal cancer who respond well to induction chemotherapy and subsequently complete total neoadjuvant therapy in order to observe the organ preservation rate after total neoadjuvant therapy.

Researchers are encouraged to apply for the full study protocol, study data, and analytic code upon reasonable request by contacting the primary investigator (Ziqiang Wang).