Diagnostic value of 18FAlF-NOTA-FAPI-04 PET/CT in breast cancer: comparison with conventional imaging

Background Conventional imaging has limitations in differentiating benign from malignant breast lesions and in staging breast cancer (BC). This study compared the diagnostic and staging performance of 18 FAlF-NOTA-FAPI-04 PET/CT with conventional imaging in suspected breast lesions. Methods This single-center post hoc retrospective analysis included therapy-naïve participants with suspected breast lesions who underwent 18 FAlF-NOTA-FAPI-04 PET/CT between July 2023 and February 2025. All patients underwent ultrasonography, mammography, breast MRI, whole-body CT, and bone scan. Conventional imaging results were based on consensus visual interpretation integrating these modalities. PET/CT images were assessed visually and semi-quantitatively to assess the diagnostic accuracy. Lesions were confirmed by histopathology and follow-up (median, 4.5 months). Diagnostic performance for primary breast lesions, regional lymph nodes metastases (LNM), and distant metastases was evaluated on lesion-based, whereas visual scoring and staging (the AJCC eighth edition) comparisons were patient-based. Receiver operating characteristic/Delong and McNemar χ² analyses were performed using SPSS Statistics 29.0. A two-sided P 0.05 was statistically significant. Results Sixty-nine women (median age, 50 years) with 81 breast lesions, 797 regional lymph nodes, and 94 distant metastases were included, and all 69 patients underwent ultrasonography, mammography, breast MRI, whole-body CT, and bone scan. For primary breast lesions, conventional imaging showed sensitivity and specificity of 93.75% and 100.00%, whereas visual PET/CT showed 98.44% and 70.59%. Although LBR breast achieved the highest area under the curve (AUC), its AUC was not significantly different from that of conventional imaging (1.000 vs. 0.970, P = 0.078). In contrast, visual PET/CT showed a significantly lower AUC than conventional imaging (0.845 vs. 0.970, P = 0.034). For regional LNM detection, visual PET/CT achieved sensitivity and specificity of 95.95% and 97.60%, which were significantly higher than the corresponding values of conventional imaging (73.99% and 95.41%, all P 0.05). PET/CT detected all 94 distant metastases, and patient-based visual scores favored PET/CT over conventional imaging (52 vs. 34). PET/CT also improved the accuracy in predicting pathological N staging (91.43% vs. 65.71%, P = 0.008) and final staging (74.29% vs. 45.71%, P = 0.009). Conclusions 18 FAlF-NOTA-FAPI-04 PET/CT outperforms conventional imaging in detecting regional LNM and improving pathological staging accuracy in BC.