Patients included in the study went through standard preoperative preparation and were informed about potential conversion to open surgery. The procedure started with LUS performed according to the department's standard guidelines (one twelve mm trocar in the midline and one 12 mm trocar in the left upper quadrant) followed by a stepwise scanning of relevant structures (e.g. liver, pancreas, retroperitoneum) with dedicated laparoscopic ultrasound equipment (BK Medical, Herlev, Denmark). If the suspected lesion(s) was detected by LUS in the relevant area (according to preoperative imaging), laparoscopic resection was attempted, and if successful the specimen was removed in an eEndo-bBag (Kebomed, Denmark) through one of the trocars. A second LUS was performed to ensure that no tumor was left behind ("loss-of-lesion(s)").

If any problem occurred during the laparoscopic procedure, the operation was converted to an open procedure. Prophylactic antibiotics were not given routinely but were administered during surgery at the surgeons' discretion.

The intra- and postoperative course and final clinical outcome including pathology reports were retrieved from the patient's electronical records. This included a postoperative follow up of at least 12 months to investigate potential incomplete resection. Postoperative complications were graded according to Dindo-Clavien (17). The pathology reports were retrieved from the Danish Pathology Registry.

Inclusion Criteria:

Patients with intra- and retroperitoneal tumor(s) (IRT) detected by imaging (US/CTMR/PET or EUS) and a clinical indication for explorative laparotomy

Exclusion Criteria:

Patients with contraindications for laparoscopy, such as severe adherences were excluded

The patients were discussed at the Upper or Lower GI Multidisciplinary Team conferences MDT in order to make sure that only patients where explorative laparotomy was considered the next and only possible clinical step, were referred for the minimal invasive procedure.