Local Excision for Organ Preservation in Early REctal Cancer With No Adjuvant Treatment

Inclusion Criteria: * Patients age 18 years or older. * Histologic proof of infiltrating rectal adenocarcinoma. or * Preoperative biopsy compatible with rectal adenoma or intramucous adenocarcinoma with endoscopic or radiological suspicion of infiltrating adenocarcinoma. 1. Endoscopic criteria: Kudo´s crypt pattern of V or higher, despite non confirmatory preoperative histology. endoscópicos: patrón de criptas V o superior según la clasificación de Kudo, que define lesiones infiltrantes, a pesar de que la histología preoperatoria no sea confirmatoria . 2. Ultrasonographic criteria: hipoecogenic rectal tumor invading the intermediate hyperecogenic layer (submucosal), but does not infiltrate the hypoecogenic outer layer (muscularis propia). 3. Radiological criterio in MR: tumor invades the submucosal layer without infiltration of the rectal muscularis propia. The usual low signal submucosal image is substituted with an aberrant signal, meaning the loss of the zebra pattern in a normal rectal wall. * Rectal neoplasm with an inferior limit no further than 2cm proximal to the anorectal verge, both in digital rectal examination and in radiology examinations, ideally magnetic resonance (MR). * Rectal neoplasms up to 3 cm of major diameter. * Clinical preoperative staging of cT1N0M0, based on endoscopy, MR, +/- endorectal ultrasound. * Cases in which LE as exclusive treatment with curative intent is prescribed after MDT discusión, regardless of the approach both via flexible endoscopy and transanal endoscopic microsurgery and its variations. * Neoplasms with low risk histologic criteria known preoperatively or lack of information regarding this aspect: 1. Submucosal infiltration of less than 1000µm (sm1 in the Kikuchi classification) . 2. Tumor budding absent. 3. En bloc resection in patients with a previous endoscopic resection. 4. Vascular, lymphatic and perineural invasión absent. 5. Low histologic grade. Exclusion Criteria: * Patients younger than 18 years old. * Rectal neoplasms different from adenocarcinoma. * Neoplasms in which the inferior edge is farther than 2cm proximal to the anorectal verge in the preoperative MR. * Any other clinical stage other than cT1N0M0 (any T\>1, N+, or M+). * Neoplasms larger than 3cm. * Preoperatively demonstration of PPHF: 1. Submucosal infiltration deeper than 1000µm (sm2 and sm3 in the Kikuchi classification) 2. Tumor budding present. 3. Piecemeal resection in cases with previous endoscopic resection. 4. Vascular, lymphatic and perineural invasión presence. 5. High histologic grade. * Any patient with planned systemic treatment with RTQT combined with the LE after MDT discusión, regardless of the preoperative clinical or postoperative pathological stage.