interim analysis

Smaller submucosal tumors (SMT) in the stomach are usually seen as an incidental finding during a gastroscopy, although current diagnostics usually do not clearly indicate what type of tumor it is. In summary, there is no good evidence for dealing with SMT. In this study, an endoscopic full-thickness resection, primarily with the FTRD device, is to be offered to all patients with gastric SMT without a confirmed histology seen in a certain period of time . Patients who do not want to take advantage of this are included in a systematic follow-up program.

The investigators hope to learn about the rate of so-called GIST tumors and other histologies, as well as the rate of change in the follow-up group.

Also, study contents will be accuracy of endosonographic imaging and puncture in comparison with resection histology, technical feasibility and histological completeness of the FTRD- based endoscopic (full-wall) resection option, complications of such a resection (secondary bleeding and dehiscences), and patient preferences with standardized information.

Smaller submucous tumors in the stomach are usually seen as a random finding in gastroscopies and present a diagnostic dilemma to the doctor and patient:

type specification is usually unclear whether it is an absolutely benign (without degeneration potential) or a malignant or prone tumor (usually gastrointestinal stromal tumor, GIST). However, this is crucial for further management.

In endosonographic imaging there are only approximate values in the differential diagnosis between GIST and non-GIST, the endoscopic biopsy is too superficial, and the hit rate of endosonographic pin puncture is limited, and in most studies is less than 70% Therefore, one can only make assumptions and create a risk profile from imaging and tumor size (limit size 3 cm, partly also 2 cm). Both follow-up recommendations (rather no GIST) and laparoscopic surgical removal (proven or probable/possible GIST) are not rarely without clear preference, especially for smaller tumors.

For these indications, a simple endoscopic removal option comparable to the polypectomy in the colon (where no histological type diagnosis is made before) does not exist.

Previous studies are usually subject to bias in several directions:

1. The frequency of GIST tumors among submucous tumors/lesions (SMT) in the stomach is unclear. Gastroenterological series always contain smaller GIST tumors, but are reported almost exclusively from clinics. The rate of these tumors in the overall collective of patients seen in the field of (mostly established) gastroenterologists is thus completely unclear. Surgical or oncological series have usually included more aggressive tumors consisting mainly or exclusively of GIST tumors, therefore do not allow epidemiological conclusions.
2. If no surgery is performed (and thus a definitive histology is forced), only information from follow-up examinations remains. Previous follow-up studies show the dilemma of insufficient differential diagnosis of lesions by endosonography and (endosonographic or other) biopsy, which usually have insufficient accuracy. In addition, the follow-up time in the studies hardly extends beyond 2 years. The "gastroenterological gut instinct" that these small lesions are not dangerous may be true, but is not proven.

Inclusion Criteria:

• Patients with endoscopically diagnosed and endosonographically confirmed submucosal tumors of 0.5 to 2 cm in the stomach without definitive histology / cytology
• Initial diagnosis less than 2 years ago
• No contraindication to endoscopic resection
• Patient's informed consent

Exclusion Criteria:

• Tumor size > 2 cm
• Tumors with proven / suspected malignancy for which oncologically no endoscopic resection should be performed, i.e. for which oncological or surgical therapy is planned
• SMT known > 2 Years
• Patients with severe general illnesses (limited operability) or malignancies
• Clotting disorders
• Pregnancy