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

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 ⁶⁸ Ga-FAPI-04 PET/CT and ¹⁸ F-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. SUV _Max values of primary and metastatic lesions were recorded, and the results were subjected to statistical analysis. Results; When the primary lesion ¹⁸ F-FDG SUV _Max (8.1±5.8) was compared with ⁶⁸ Ga-FAPI SUV _Max (15.43±6.4), ⁶⁸ Ga-FAPI SUV _Max was higher (p<0.0001). ¹⁸ F-FDG detected lymph node metastases in 26 patients. ¹⁸ F-FDG did not detect lymph node metastasis in 16 patients. 68Ga-FAPI detected lymph node metastases in 39 patients. ⁶⁸ Ga-FAPI failed to detect lymph node metastases in 3 patients. ⁶⁸ Ga-FAPI was more effective than ¹⁸ F-FDG in detecting axillary lymph node metastasis (p=0.02 x2=5.125). The SUV _Max values of the detected lymph nodes were higher with ⁶⁸ Ga-FAPI (10.3±5.8) than with ¹⁸ F-FDG (7.0±4.3) (p=0.015). The sensitivity of ⁶⁸ Ga-FAPI (92.86%) was higher than that of ¹⁸ F-FDG (61.9%). According to histopathologic subtypes; invasive ductal carcinoma (IDC), ⁶⁸ Ga-FAPI was higher than ¹⁸ F-FDG SUV _Max (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+ ⁶⁸ Ga-FAPI SUV _Max values were higher than the ¹⁸ F-FDG SUV _Max values (p=0.01, p<0.0001 and p=0.01, respectively). There was no difference in triple negative molecular subtypes. Conclusions: ⁶⁸ Ga-FAPI-04 PET/CT is superior to ¹⁸ F-FDG PET/CT in the detection of axillary lymph node metastasis of breast cancer with high sensitivity and high SUV _Max value.