Introduction: The standard treatment for rectal adenocarcinoma is total mesorectal excision (TME), a technique involving resection of the rectum, with or without a temporary or permanent stoma. TME is associated with high morbidity and genitourinary alterations. On the other hand, transanal endoscopic surgery (TEM) allows access to tumors up to 20 cm from the anal margin, with much lower postoperative morbidity and without the need for ostomy. For T1, N0, M0 rectal adenocarcinomas without poor prognostic factors, TEM is the technique of choice. However, recent studies have described local recurrences of up to 20%. Our group, TAUTEM, has just completed a phase III clinical trial in T2-T3ab, N0, M0 rectal cancer, comparing preoperative chemoradiotherapy (CRT) and TEM versus TME, with very positive results in terms of postoperative morbidity, quality of life, and a local recurrence rate of 7.4%, not inferior to TME.

These results encourage our TAUTEM group to launch a similar project at the T1, N0, M0 stage, comparing standard TEM treatment versus QRT and TEM, aiming to improve rectal preservation outcomes and enhance results regarding local recurrence, distant recurrence, and oncologic survival.

Method: Prospective, controlled, randomized phase III multicenter clinical trial. Patients with rectal adenocarcinoma within 10 cm of the anal margin and up to 4 cm in size, staged as T1, N0, M0, will be included. These patients will be randomized into two groups: TEM after CRT and TEM alone. Postoperative morbidity and mortality, CRT side effects, and quality of life will be recorded. The minimum follow-up will evaluate rectal preservation and local recurrence and survival at two and three years. The sample size calculation for the study will be 106 patients.

Conclusions: The aim of the study is to improve oncological outcomes in stage T1, N0, M0 rectal cancer through preoperative chemoradiotherapy associated with local surgery (TEM).

Inclusion Criteria:

• Indication by multidisciplinary committee of indication for local excision, according to ESMO and NCCN criteria.
• Rectal adenocarcinomas in the biopsy, located at a distance from the anal margin less than or equal to 10 cm measured by rigid rectoscopy at the time of ER.
• Preoperative staging by ER and pelvic MRI of T1,N0. In case of disparity, higher staging will be considered the definitive diagnosis. If it is greater than T1, it will be excluded.
• Tumors equal to or less than 4 cm in maximum diameter measured by MRI.
• ASA index equal to or less than III.
• Absence of distant metastases by abdominal CT and chest X-ray (if inconclusive, Thoracic CT)

Exclusion Criteria:

• Preoperative staging by EER or pelvic MRI higher than T1 or N0.
• Presence of distant metastases. Synchrony with other colorectal adenocarcinomas.
• Undifferentiated rectal adenocarcinomas or with the presence of poor prognostic factors in the preoperative biopsy (undifferentiated, venous, lymphatic or perineural infiltration, budding) .
• Patients with intolerance to preoperative chemotherapy or radiotherapy.
• Do not sign informed consent.

SAP, Study Protocol, Informed Consent Form (ICF)