Background: Liver metastases are common in patients with neuroendocrine neoplasms, but often underestimated by preoperative imaging. Intraoperative ultrasound (IOUS) is the reference standard for staging of primary and metastatic liver tumors, with a diagnostic accuracy superior to that of CT and MRI. Rationale: The present study aims to evaluate the contribution of IOUS to staging of liver disease in patients with neuroendocrine tumor candidates for primary tumor resection classified as cM0 at preoperative imaging.

The study will collect a prospective series of 99 patients undegoing surgery for gastro-intestinal or pancreatic neuroendocrine tumor at the Humanitas Clinical Institute (coordinating centre) or at one of the participating centres in the period 2020-2023. All patients had to be cM0 tumor at preoperative imaging. Additional inclusion criteria: age>18 years, ability to give the informed consent for study participation; no other malignancies in the previous 5 years; preoperative staging including abdominal CT and DOTATOC PET-CT performed ≤60 days before surgery.

This prospective observational multicentre study aims to elucidate the proportion of patients with gastro-intestinal or pancreatic neuroendocrine tumor cM0 at preoperative imaging that have intraoperative detection of liver metastases at IOUS.

Primary endpoint:

- Performances of IOUS in identifying liver metastases in patients with neuroendocrine tumor classified as cM0 at preoperative imaging

Secondary endpoints:

• Impact of IOUS on the therapeutic strategy
• Performances of preoperative imaging (CT, MRI and PET-CT) in comparison with those of IOUS

The study will collect a prospective series of 99 patients undergoing surgery for gastro-intestinal or pancreatic neuroendocrine tumor at the Humanitas Clinical Institute (coordinating centre) or at one of the participating centres in the period 2020-2023.

The study includes the following steps:

Preoperative / enrollment: All patients candidates to resection of gastro-intestinal or pancreatic neuroendocrine tumor will be considered for the study. Only cM0 patients will be enrolled. All patients enrolled in the study must have performed a preoperative abdominal CT scan with contrast medium and a DOTATOC-PET-CT (both performed ≤60 days before surgery).

Intraoperative: During surgery, the investigator will perform, as standard in our clinical practice, an accurate exploration of the liver by inspection, palpation and IOUS. The investigator will record the identification of any liver lesion. If one or more nodules suspect of being neuroendocrine liver metastases are identified, it will be necessary, whenever possible, as already routinely performed, to carry out a biopsy or to remove it (if superficial) for histological confirmation of the diagnosis. After completion of liver staging, the primary tumor will be resected.

Postoperative / follow-up: Enrolled patients will have standard postoperative management.

Standard statistical analyses will be performed. Per-patient and per-lesion analyses will be performed to asses performances of preoperative imaging modalities (CT, MRI, PET-CT) and of intraoperative ones (inspection, palpation, and IOUS).

Inclusion Criteria:

• Patients undergoing open or minimally-invasive surgery for primary neuroendocrine gastro-intestinal or pancreatic tumor.
• cM0 tumor at preoperative imaging
• Preoperative staging including abdominal CT and DOTATOC PET-CT
• Age ≥18 years
• No other malignancies in the previous 5 years

Exclusion Criteria:

• Preoperative imaging performed >60 days before surgery
• Patient refusal to participate the study
• Incomplete intraoperative hepatic staging (peri-hepatic adhesions, IOUs not available…)

The study will collect a prospective series of 99 patients undergoing surgery for gastro-intestinal or pancreatic neuroendocrine tumor at the Humanitas Clinical Institute (coordinating centre) or at one of the participating centres (see the Appendix for list of the centres) in the period 2020-2023.