For the millions of women living with endometriosis — often undiagnosed for years — the accuracy of initial imaging can determine whether surgical planning captures the full disease burden or leaves lesions behind. A fundamental limitation of current standard-of-care imaging is about to be seriously challenged by a molecular imaging approach targeting the biology of the disease itself.
This retrospective pilot study, published in the Journal of Nuclear Medicine, explored whether fibroblast activation protein inhibitor (FAPI) PET/MRI — using the radiotracer [68Ga]BED003 — could detect endometriotic lesions beyond what conventional MRI alone identifies. Eighteen premenopausal women were divided into a test cohort of nine with suspected or confirmed endometriosis and a reference cohort of nine without known endometriosis. Using a segment-based assessment framework derived from the #Enzian classification system, the hybrid PET/MRI modality revealed focal radiotracer uptake in lesions across anatomical segments that MRI alone failed to characterize, particularly in deep infiltrating endometriosis. Lesion detection was quantified via SUVmax and SUVmean values, with laparoscopic findings serving as ground truth where available.
The significance here lies in the mechanism: fibroblast activation protein (FAP) is upregulated in actively remodeling tissue, including ectopic endometrial implants, making FAPI tracers biologically specific to disease activity rather than merely anatomical distortion. This aligns FAPI imaging with an expanding literature demonstrating its utility in oncologic staging, now extended for the first time to a benign but functionally devastating gynecologic condition. The critical caveat is the study's small size — just nine patients in the test cohort — making this a proof-of-concept signal rather than clinical validation. The lack of menstrual-cycle synchronization for scans is also a meaningful gap, given FAP expression likely fluctuates with hormonal cycling. This is incremental but directionally important: if replicated in larger prospective cohorts, molecular imaging of endometriosis could reshape surgical planning and reduce the diagnostic odyssey that characterizes the condition.