What is the study about? This study introduces and evaluates a new endoscopic technique called Endoscopic Synchronized Injection and Submucosal Dissection (ESISD). It is designed to remove large, flat precancerous growths in the rectum, known as Granular Mixed Nodular Laterally Spreading Tumors (LST-G-M). We compared this new technique to the standard procedure, Conventional Endoscopic Submucosal Dissection (ESD), to see if it is safer, faster, and more efficient.

Who is this for? This research is intended for patients with large, flat rectal polyps, their families seeking the latest treatment options, and healthcare providers interested in advancements in minimally invasive gastroenterology procedures.

Inclusion Criteria:

1. Age ≥ 18 years.
2. Endoscopic diagnosis of a large (≥ 20 mm) granular mixed nodular laterally spreading tumor (LST-G-M) located in the rectum.
3. Lesion situated 0-15 cm from the anal verge.
4. Pre-procedure imaging (e.g., EUS) and endoscopic assessment suggest a very low to low risk of lymph node metastasis (i.e., lesions confined to the mucosa or with superficial submucosal invasion < 1000 μm).
5. Deemed suitable for Endoscopic Submucosal Dissection (ESD) based on a comprehensive clinical evaluation by the endoscopist.
6. Provision of signed and dated informed consent form.

Exclusion Criteria:

1. Coagulopathy that cannot be adequately corrected, including an international normalized ratio (INR) > 1.5 or a platelet count < 50,000/μL.
2. Evidence of deep submucosal invasion (≥ 1000 μm) or obvious non-lifting sign, suggesting a need for surgical intervention.
3. Pregnancy or lactation.
4. Inability to tolerate deep sedation or general anesthesia.
5. History of colorectal surgery (except for simple appendectomy or polypectomy).
6. Presence of a synchronous colorectal cancer that requires priority treatment.
7. Recurrent lesions at the same site.
8. Any condition that, in the investigator's opinion, could increase the patient's risk or interfere with the study assessments.