Diagnostic Performance of ⁶⁸Ga-FAPI PET/CT Versus ¹⁸F-FDG PET/CT in Evaluating Neoadjuvant Therapy Pathological...

Accurate pathological response assessment of breast cancer following neoadjuvant therapy (NAT) is clinically critical but lacks robust imaging methods, so this study evaluated the diagnostic accuracy of ¹⁸F-fluorodeoxyglucose (FDG) PET/CT and ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI) PET/CT in clinically node positive (cN+) breast cancer patients receiving NAT. This prospective study enrolled pathologically confirmed breast cancer patients who underwent NAT and both PET/CT scans preoperatively. The maximum standardized uptake value (SUVmax) was measured and an optimal ⁶⁸Ga-FAPI PET/CT threshold was determined via receiver operating characteristic (ROC) curve analysis. Among 75 patients, 33 (44.0%) achieved pathological complete response (pCR). SUVmax was significantly lower in the ypT0/Tis group compared to the ypT+ group for both ¹⁸F-FDG PET/CT (1.45 ± 0.55 vs. 5.19 ± 4.69, p < 0.001) and ⁶⁸Ga-FAPI PET/CT (1.59 ± 1.22 vs. 10.45 ± 8.54, p < 0.001). In the overall cohort, ⁶⁸Ga-FAPI PET/CT demonstrated higher sensitivity in detecting residual disease compared to ¹⁸F-FDG PET/CT (0.8 vs. 0.6, p = 0.003), with comparable specificity (0.9 vs. 0.9, p = 1.00). Exploratory subgroup analysis found that ⁶⁸Ga-FAPI PET/CT had superior sensitivity compared to ¹⁸F-FDG PET/CT in the hormone receptor-positive (HR + ) group (0.8 vs. 0.6, p = 0.02). These findings show that ⁶⁸Ga-FAPI PET/CT outperforms ¹⁸F-FDG PET/CT in identifying residual breast lesions after NAT in cN+ patients, particularly among HR+ patients, which would guide further treatment strategies after NAT.