This is a prospective, phase II, non-randomized clinical imaging trial. Ga68-FAPI-46 is a novel radiotracer used in PET/CT imaging, targeting a protein of the tumor microenvironment called FAP (Fibroblast activation protein).

The aim of the study is to assess the accuracy of Ga68-FAPI-46 PET/CT for preoperative assessment of peritoneal carcinomatosis in colorectal and ovarian cancer.

Fibroblast activation protein (FAP) is a type II transmembrane glycoprotein expressed on the surface of cancer-associated fibroblasts (CAFs) in the stroma of various tumor entities. Recently, radiolabeled molecules targeting the FAP, called FAP inhibitors (FAPI) labelled with Gallium-68, have been developed for molecular imaging with PET/CT (positron emission tomography/computed tomography). This radiotracer often presents a higher cancer lesion detectability than F18-FDG (fluorodeoxyglucose), partly thanks to its higher tumour-to-background ratio achieved by a low background activity, particularly in the brain, abdominal cavity and liver. These advantages have resulted in a superior sensitivity of Ga68-FAPI PET/CT over F18-FDG and higher SUV (standardized uptake value) in evaluating various types of cancer. In this context, Ga68-FAPI PET/CT seems promising to further study as a clinical imaging modality for preoperative assessment of peritoneal carcinomatosis.

In this study, the investigators correlate Ga68-FAPI PET/CT findings in terms of peritoneal involvement with intraoperative findings based on histopathology and try to find out how accurate Ga68-FAPI PET/CT is for the preoperative assessment of peritoneal carcinomatosis.

Inclusion Criteria:

• Histologically proven colorectal and ovarian cancer.
• Known or suspected peritoneal metastases from the tumour of origin.
• Scheduled for peritoneal complete cytoreductive surgery with curative intent with or without neoadjuvant chemotherapy.
• ECOG (Eastern Cooperative Oncology Group) Performance status ≤2.
• Signed written informed consent obtained before any study-specific screening procedures.

Exclusion Criteria:

• Non-resectable extra-abdominal metastasis and/or >3 hepatic metastases on standard work-up
• Known chronic inflammatory conditions including the intestinal system (eg. inflammatory bowel disease, Crohn's disease)
• Pregnant and lactating women
• Previous or concurrent malignancy diagnosed within the last 3 years except adequately treated in situ carcinoma of the cervix uteri and basal or squamous cell skin cancer.
• Subjects with another significant medical condition which, in the investigator's opinion, may interfere with the completion of the study.