68 Ga-FAPI-04 PET/CT for Detection of Locoregional Lymph Node Metastases in Gynecologic Squamous Cell Carcinoma

Background/Aim: Detection of locoregional lymph node (LN) metastases is a critical prognostic factor in gynecologic squamous cell carcinoma (SCC). Contrast-enhanced computed tomography (CT) is limited by insufficient specificity, potentially leading to overtreatment. We evaluated gallium-68 fibroblast activation protein inhibitor (68Ga-FAPI-04) positron-emission tomography (PET)/CT for the detection of locoregional LN metastases in this setting, using CT as comparator. Patients and Methods: In this retrospective single-center study, 68Ga-FAPI-04 PET/CT scans of 15 patients with gynecologic SCC (nine cervical, six vulvar carcinomas; mean age 56.3 years, range=38-86 years) were analyzed. PET/CT and CT were read independently by two blinded readers. Histopathology and/or clinical and radiological follow-up (12-18 months) served as the reference standard. Diagnostic performance was calculated on a patient-based level; maximum standardized uptake values (SUVmax) were compared using Welch’s t-test and the Mann-Whitney U-test. Results: Histopathological confirmation was available in 12 patients; three were classified by follow-up. LN metastases were confirmed in five patients. 68Ga-FAPI-04 PET/CT achieved a sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of 100%. CT achieved a sensitivity and NPV of 100% but produced false-positive findings in three patients (specificity=70%, PPV=62.5%, accuracy=80%), caused by tattoo-associated lymphadenopathy, sarcoidosis and reactive nodal enlargement, none of which showed pathological tracer uptake. Metastatic LNs exhibited higher SUVmax (mean 23.2±6.0) than nodes false-positive on CT (mean 4.5±4.6; p=0.004 and p=0.036). Primary tumors were visualized in all patients undergoing initial staging; peritoneal nodules down to 7 mm were detected. Conclusion: In this small cohort, 68Ga-FAPI-04 PET/CT showed a higher observed specificity than contrast-enhanced CT for the detection of locoregional LN metastases in gynecologic SCC, with no false-negative cases observed.