FAPI PET in inflammatory bowel disease: a novel window on fibroblast activity, with unanswered clinical questions.

Accurate assessment of inflammatory activity in inflammatory bowel diseases (IBD) such as Crohn's disease (CD) and ulcerative colitis (UC) remains a major clinical challenge. Positron emission tomography (PET) with fibroblast activation protein inhibitors (FAPI) has recently attracted considerable interest for its ability to visualize fibroblast-associated tissue remodeling and stromal activation in inflammatory conditions. In the study under evaluation, Debus et al. report a retrospective pilot study of [68Ga]Ga-FAPI-46 PET/CT for noninvasive characterization and activity assessment of CD and UC. Forty-three histologically confirmed IBD patients (20 CD and 23 UC) and 43 matched controls underwent dynamic abdominal (60 min) and whole-body [68Ga]Ga-FAPI-46 PET/CT to quantify FAPI uptake, kinetics, and lesion burden, with imaging findings compared with colonoscopy. They found significantly higher FAPI uptake in both FAPI-positive lesions and in many 'healthy-appearing' gut segments of IBD patients versus controls; uptake was greater in active versus inactive disease, and lesions displayed two characteristic kinetic patterns that can further stratify inflammatory disease. The study is an important, hypothesis-generating contribution that supports the feasibility and biological plausibility of FAPI PET for IBD, but its retrospective design, modest sample size, limited histologic lesion-level correlation and control selection temper conclusions about diagnostic performance and clinical utility.