The value of serial [⁶⁸Ga]Ga-FAPI-04 PET/CT in predicting pathological response and evaluating therapeutic efficacy to neoadjuvant chemotherapy in breast cancer.

OBJECTIVE To investigate the clinical utility of serial [⁶⁸Ga]Ga-FAPI-04 PET/CT for predicting pathological response and evaluating therapeutic efficacy in breast cancer (BC) patients receiving neoadjuvant chemotherapy (NAC). METHODS A total of 64 biopsy-confirmed patients with BC were retrospectively included. Serial [68Ga]Ga-FAPI-04 PET/CT scans were conducted at three time points: prior to NAC (baseline, PET1), after two cycles of NAC (interim, PET2), and before surgery (pre-surgery, PET3). PET/CT parameters derived from the primary BC lesions were recorded before and after NAC. The changes in these parameters were compared between the pathological complete response (pCR) and the non-pCR group. Logistic regression was used to assess the predictive value of [68Ga]Ga-FAPI-04 PET/CT parameters for predicting pCR. Receiver operating characteristic (ROC) curve analysis was employed to determine the optimal cutoff values for predicting pCR. DeLong's test was applied to statistically assess differences in the area under the ROC curves (AUC). RESULTS Significant reductions in [68Ga]Ga-FAPI-04 PET/CT parameters (ΔSUVmax, ΔSUVmean, ΔFTV, ΔTLF) were observed among all patients, with significantly greater decreases in the pCR group compared to the non-pCR group (all P < 0.001). In the non-pCR group, the total FTV (ΔtFTV1-2 and ΔtFTV1-3) of primary breast lesions and metastatic lymph nodes showed moderate correlation with the residual cancer burden (RCB) score. Multivariate logistic regression identified ΔSUVmean1-2 (P = 0.027), ΔFTV1-2 (P = 0.006), ΔSUVmean1-3 (P = 0.032), and ΔFTV1-3 (P = 0.010) as independent predictors for predicting pCR. On the basis of the ROC curve analysis, ΔSUVmean1-3 (AUC = 0.848) and ΔFTV1-3 (AUC = 0.906) showed slightly higher predictive performance than ΔSUVmean1-2 (AUC = 0.825) and ΔFTV1-2 (AUC = 0.869), respectively, but the difference was not statistically significant (P > 0.05). CONCLUSION This study demonstrates that serial [68Ga]Ga-FAPI-04 PET/CT facilitates early prediction of pathological response to neoadjuvant chemotherapy in breast cancer, as well as assessment of therapeutic efficacy. Prospective studies with larger samples are needed.