FAP-targeted PET imaging in peritoneal carcinomatosis

Peritoneal carcinomatosis remains a major determinant of prognosis and operability in abdominopelvic malignancies, yet conventional CT/MRI and Fluorine-18([18F])-FDG PET/CT frequently underestimate peritoneal disease extent, particularly for small, flat, or low-FDG-avid implants. Fibroblast activation protein inhibitor (FAPI) PET targets cancer-associated fibroblasts within the tumour stroma and typically provides high tumour-to-background contrast, particularly in the abdomen. Across head-to-head studies and meta-analyses, FAPI PET/CT consistently demonstrates higher tumour uptake and tumour-to-background ratios in peritoneal lesions and higher diagnostic sensitivity than FDG PET/CT, with a downstream increase in imaging-derived peritoneal cancer index that shows the extent of the peritoneal disease. Emerging evidence suggests that improved peritoneal metastases mapping can meaningfully influence clinical decision-making by refining patient selection for cytoreductive surgery and intraperitoneal/systemic therapies and by reducing the risk of understaging. Current limitations include a predominance of single-centre data in cohorts with a high pre-test probability of peritoneal disease, heterogeneous reference standards, and potential false positives from benign fibro-inflammatory or reparative processes. Ongoing prospective trials, further comparisons with CT/MRI (including PET/MRI), implementation studies, and health-economic evaluations will be essential to define optimal indications and confirm outcome-relevant benefit.