A prospective comparison of early versus late ¹⁸F-FAPI-04 PET/CT imaging for breast cancer diagnosis

¹⁸Fluorine (¹⁸F) labeled inhibitors of fibroblast activation protein (¹⁸F-FAPI) PET/CT is an emerging molecular imaging technique suitable for patients with breast cancer (BC). However, some patients may not tolerate the long waiting time after injection, making it crucial to assess whether early imaging can provide sufficient clinical diagnostic information. In this prospective study, 40 patients with suspected BC underwent dual-phase ¹⁸F-FAPI-04 PET/CT at ~ 10 min (early) and ~ 60 min (late) post-injection. The diagnostic performance of both protocols was compared in differentiating benign from malignant lesions. A total of 51 breast lesions were detected, and SUVmax and lesion-to-background ratio (LBR) were obtained by outlining ROIs. After the PET/CT scan, all lesions underwent tissue biopsy, with 36 being BC and 15 being benign breast lesions (BBL). The results showed a significant difference in SUVmax between early and late imaging (p = 0.001), but no significant difference in LBR (p = 0.456). The ¹⁸F-FAPI-04 uptake in the BC group was significantly higher than in the BBL group. The cutoff values for SUVmax were 3.62 for early imaging and 4.12 for late imaging, while the cutoff values for LBR were 4.42 for early imaging and 4.34 for late imaging. At the optimal cutoff values, early imaging with SUVmax achieved the highest diagnostic performance, with an AUC of 1.00, and both sensitivity and specificity of 100%. The AUC for LBR was 0.93, with a sensitivity of 86.1% and specificity of 86.7%. No significant difference in diagnostic performance was found between early and late imaging (DeLong test; SUVmax p = 0.48 and LBR p = 0.25). Our findings indicate that early ¹⁸F-FAPI-04 PET/CT imaging offers diagnostic accuracy comparable to late imaging while significantly reducing acquisition time, supporting its potential as a practical alternative in clinical practice.