The standard treatment for advanced gastric cancer without metastases is gastrectomy, where the whole stomach or a large proportion is removed surgically together with regional lymph nodes. Some patients cannot tolerate this invasive procedure because of old age or comorbidities. A tumor left in place can cause local symptoms such as bleeding or outlet obstruction. In this study, the investigators want to test the safety and feasibility of Laparoscopic and Endoscopic Collaborative Surgery (LECS) as a less invasive treatment option to locally remove gastric tumors without requiring extensive surgery in these frail patients. LECS is a minimally invasive surgical technique where the tumor margin is first marked from the inside with a gastroscope, followed by surgical removal of the lesion under endoscopic guidance.

In patients with advanced gastric cancer (AGC), laparoscopic gastrectomy with lymph node dissection in combination with chemotherapy is the recommended treatment for cases with curative intent. However, some patients cannot tolerate such demanding treatment because of comorbidities or advanced age. If gastrectomy or palliative chemotherapy cannot be offered the only remaining alternative is best supportive care.

Patients with AGC that cannot receive definitive surgical or oncological treatment can develop complications such as bleeding from the primary tumor or gastric outlet obstruction. Such complications can be difficult to manage by endoscopic means, and significantly impact the patients' quality of life.

Laparoscopic and endoscopic collaborative surgery (LECS) was reported by Hiki et al in 2008 as a treatment for submucosal tumors. With this method, the endoscopist first performs mucosal incision around the tumor followed by laparoscopic removal of the tumor with endoscopic guidance.

In Japan, the current indication for LECS is gastrointestinal stromal cell tumors with a size of 2-5 cm. LECS has also been described in two case reports as palliative treatment for patients with AGC without being in a state to undergo gastrectomy. To the best of the investigators' knowledge, no prospective trial has studied LECS for this indication. Compared with gastrectomy, LECS is a very safe and much less invasive technique with few severe adverse events. If the tumor could be completely resected with LECS, the risk for bleeding and other tumor-related complications could be diminished which could significantly benefit the patients and improve their quality of life.

In this study, the investigators want to test the safety and feasibility of performing LECS for patients who are unfit for standard treatment with gastrectomy. The patients will be screened for inclusion through a multidisciplinary team meeting. If they meet the inclusion criteria they will be asked to participate in the study on an outpatient meeting with a member of the research team. If the patient agrees to participate and can sign an informed consent, they will be booked for a LECS procedure. After the operation is performed, the patient will meet the researcher again 4-6 weeks later and will be asked to fill in two QoL questionnaires.

Inclusion Criteria:

• pT2-T4aN0M0 gastric carcinoma
• Borrmann type 1-2 < 5 cm or Borrmann type 3 < 2 cm
• Patient assessment by the multidisciplinary tumor board as not fit for gastrectomy
• Signed informed consent

Exclusion Criteria:

• Borrman type 4
• Location in the cardia