The objetive of this clinical trial is to evaluate the efficacy and safety of a solution for endoscopic mucosal resection of colonic lesions in patients undergoing endoscopic resection procedures.

The main questions it aims to answer are:

Does the investigational solution improve the efficacy of endoscopic mucosal resection compared to standard practice? Is the investigational solution safe for use in colonic lesion resection procedures?

Researchers will compare the investigational solution (Demirex) to a standard or placebo solution to see if it improves procedural outcomes and safety profiles.

Participants will undergo endoscopic mucosal resection using either the investigational solution or the comparator, and will be monitored for procedural success, safety, and any adverse events.

Inclusion Criteria:

• Patients of any sex, >18 years old, diagnosed with sessile or flat polyps, with a diameter greater than or equal to 2 cm, in the intestinal submucosa by the Endoscopy Unit.
• The subject has understood and signed an informed consent form (ICF) approved by a Research Ethics Committee (REC) before any study evaluation and commits to completing the study as defined in the protocol.
• Not undergoing active treatment with antiplatelet or anticoagulant drugs.
• After signing the informed consent, patients are scheduled for lesion resection within <3 months from their diagnosis.

Exclusion Criteria:

• Patients with documented allergy to any of the components of the mucosectomy solution or drugs used in sedation.
• Pregnant women.
• Patients on contraceptive treatment or post-menopausal.
• Hematological disorders with uncorrected coagulation abnormalities, with an INR >= 1.5, or patients undergoing active treatment with antiplatelet or anticoagulant drugs.
• Patients with intestinal perforation or obstruction, toxic megacolon, diverticulitis, or inflammatory bowel disease.
• Patients with previous partial resection or pending resection.
• Patients with lesions classified as Paris type III and/or invasive intestinal carcinoma and/or metastases. Patients with previous treatment of the lesion (radiotherapy, endoscopic, surgical, chemotherapy).
• Patients included in another study during the previous month.
• Conditions that, in the medical judgment, contraindicate polyp removal.
• Absence of a signed informed consent, non-acceptance, or contraindication of surgical or anesthetic techniques (Patients with ASA status: High anesthetic risk (ASA score > 3)) and difficulty in the patient's understanding of the conditions of the endoscopic procedure.
• Endoscopic appearance of invasive malignancy.

This study is a double-blind, randomized clinical trial, meaning that participants and investigators are unaware of the treatment allocation. The investigational solution and the comparator (placebo or treatment) are identical in appearance, volume, and administration method to ensure blinding. Unblinding will only occur in cases of medical necessity.