1. Introduction The aim of the study is to evaluate the efficacy and safety of ESD by use of a new water-jet assisted ESD system using the HybridKnife® in patients with early gastric neoplastic lesions in comparison to the conventional ESD established in Japan. The water-assisted ESD technology allows pressure controlled injection of fluids through the tip of a recently developed HybridKnife®. Submucosal injection, circumferential cutting and dissection of lesions as well as coagulation of bleeding can be performed with the same device without need for changing the instrument. These options should accelerate the procedure and may increase its safety and efficacy.
2. Hypothesis The water-jet assisted ESD technique using the HybridKnife® bears the advantage of less instrument changes due to the combination of high-frequency cutting and water-jet application in one single instrument. This should lead to a simplified ESD procedure, shorter learn-ing curve and especially to a shorter procedure time.

The water-jet assisted ESD technique should be shorter than the conventional ESD techniques using IT2-, Dual- and Hook-Knifes at least with the same safety and effectiveness.

Inclusion Criteria:

• adults (≥ 18 years) with confirmed diagnosis of gastric adenoma or early gastric adenocarcinoma
• differentiated mucosal adenocarinoma without ulcer findings ≤ 60 mm in diameter.
• Lesions with ulceration ≤ 30 mm in diameter.
• undifferentiated type of mucosal cancer is ≤ 20 mm.
• The patient has given written informed consent.

Exclusion Criteria:

• pregnancy
• coagulopathy (INR>2.0, platelets < 70/nl)
• mucosal lesions which did not meet the inclusion criteria
• evidence of local or distant metastases according to endoscopic ultrasound (EUS) and/or CT scan, EUS (7.5 MHz probe) findings of tumor infiltration into deep layers of the submucosa or muscularis propria. -Patients unfit for deep sedation by use of propofol