The SUBMO-PIC01-2025 study evaluates whether SUBMO®, a submucosal injection hydrogel composed of high-molecular weight hyaluronic acid and methylene blue, is as effective and safe as normal saline for endoscopic resection of superficial colorectal lesions larger than 10 mm. Its primary aim is to determine non-inferiority in complete resection rates, whether en bloc or fragmented, and to assess safety through the systematic identification of serious adverse events. Secondary aims include analysing the total volume of product needed, the number of injections required, the maintenance of the submucosal cushion, the duration of the procedure, the ease of resection, the subjective evaluation of endoscopists, and the appearance of additional adverse events related to the intervention such as intraprocedural bleeding, fever, significant post-procedure pain, post-coagulation syndrome or immediate or delayed perforation.

Eligible participants are adults aged 18 or older with a confirmed colorectal lesion greater than 10 mm that is technically resectable using EMR or ESD, who are capable and willing to follow the study procedures and who have signed informed consent prior to any protocol-specific action. Exclusion criteria include severe comorbidities corresponding to ASA IV or V unless specifically authorised by anaesthesia, coagulopathies that prevent endoscopic resection, endoscopic suspicion of invasive cancer, any condition deemed by investigators to compromise safety or adherence, known allergy to hyaluronic acid, methylene blue or excipients, contraindications to colonoscopy or sedation, participation in another clinical investigation within the previous 30 days, and pregnancy or breastfeeding. Participants may be withdrawn due to voluntary consent withdrawal, safety concerns, protocol deviations that affect data integrity or patient safety, loss to follow-up or pregnancy discovered during the study.

The main efficacy variable is the technical success of resection as judged immediately by the endoscopist, while the main safety variable is the incidence of serious adverse events and their causal relationship with the investigational product. Exploratory variables include baseline demographics such as age, sex, ethnic origin and body mass index, anticoagulant or antiplatelet medication, and comorbidities including endoscopic history, obesity, hypertension, cardiovascular disease, haematologic disorders such as von Willebrand disease or haemophilia, and chronic liver disease. Baseline variables also include ASA classification and lifestyle habits. Polyp-related variables include size, number, anatomical location in the colon or rectum, LST subtype and JNET classification. Resection-related variables capture the technique used (EMR or ESD), whether the resection is en bloc or piecemeal, the number of fragments for calculating the Sydney Resection Quotient, the DMI score and any closure technique or complications. Treatment-related variables include total and per-surface area injection volume, number of submucosal injections needed, macroscopic evaluation of cushion maintenance, total procedure time, ease of resection using a visual analogue scale from 0 to 100, a usability questionnaire completed by the endoscopists and a detailed record of all adverse events including bleeding, fever, pain, post-coagulation syndrome and perforation.

Inclusion Criteria:

• Subjects >18 years old.
• Presence of a colorectal lesion larger than 10 mm, confirmed through colonoscopy.
• The lesion must be considered technically resectable using either Endoscopic Mucosal Resection (RME) or Endoscopic Submucosal Dissection (DSE).
• The participant must be willing and able to comply with all required study visits and procedures, according to the protocol.
• The participant must understand, sign, and date the written informed consent form before undergoing any study-specific procedures.

Exclusion Criteria:

• Severe comorbidities according to clinical judgment, including patients classified as ASA IV or ASA V, except those ASA IV cases explicitly approved as clinically safe by the center's Anesthesiology Service (using the ASA anesthetic classification).
• Patients presenting some coagulopathy that prevents safe endoscopic resection.
• Lesions that are suspicious endoscopic invasive cancer.
• Any medical condition that, in the investigator's opinion, could compromise patient safety or protocol adherence.
• Known allergy or hypersensitivity to any component of the investigational product, including hyaluronic acid, methylene blue, or any excipients.
• Contraindications to colonoscopy or to the administration of sedation/anesthesia.
• Current participation in another clinical investigation with an investigational product, or participation in any clinical study (with tested or untested products) within the previous 30 days prior to randomization.
• Pregnant or breastfeeding women.