Comparison of 68Ga-FAPI PET/CT and 18F-FDG PET/CT for Staging of the Axillary Lymph Nodes in Breast Cancer Patients

Abstract Objective: Breast cancer (BC) ranks among the most frequently diagnosed malignancies worldwide. Therefore, a reliable and accurate staging tool is essential. PET/CT is a diagnostic radioisotropic modality used in the diagnosis of BC. The objective of this study was to compare the diagnostic value of ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT in assessing primary breast tumors and axillary lymph node metastases. Methods; This retrospective study included forty-two female patients with histopathologically confirmed axillary lymph node metastases. All participants underwent both FDG and FAPI PET/CT imaging within the same week. SUVMax values of primary and metastatic lesions were recorded, and the results were subjected to statistical analysis. Results; When the primary lesion ¹⁸ F-FDG SUVMax (8.1±5.8) was compared with ⁶⁸Ga-FAPI SUVMax(15.43±6.4), ⁶⁸Ga-FAPI SUVMax was higher (p<0.0001). ¹⁸F-FDG detected lymph node metastases in 26 patients. ¹⁸F-FDG did not detect lymph node metastasis in 16 patients. 68Ga-FAPI detected lymph node metastases in 39 patients. ⁶⁸Ga-FAPI failed to detect lymph node metastases in 3 patients. ⁶⁸Ga-FAPI was more effective than ¹⁸F-FDG in detecting axillary lymph node metastasis (p=0.02 x2=5.125). The SUVMax values of the detected lymph nodes were higher with ⁶⁸Ga-FAPI (10.3±5.8) than with ¹⁸F-FDG (7.0±4.3) (p=0.015). The sensitivity of ⁶⁸Ga-FAPI (92.86%) was higher than that of ¹⁸F-FDG (61.9%). According to histopathologic subtypes; invasive ductal carcinoma (IDC), ⁶⁸Ga-FAPI was higher than ¹⁸F-FDG SUVMax (p<0.0001). Histopathologic subtypes of invasive lobular carcinoma (ILC) and invasive mucinous carcinoma (IMC) did not differ. According to molecular subtypes, the luminal A, luminal B and Her2+ ⁶⁸Ga-FAPI SUVMax values were higher than the ¹⁸F-FDG SUVMax values (p=0.01, p<0.0001 and p=0.01, respectively). There was no difference in triple negative molecular subtypes. Conclusions: ⁶⁸Ga-FAPI-04 PET/CT is superior to ¹⁸F-FDG PET/CT in the detection of axillary lymph node metastasis of breast cancer with high sensitivity and high SUVMax value.