Comparison of 68ga fapi pet/ct and 18f-fdg pet/ct in primary staging of breast cancer.

PURPOSE: To evaluate the role of 68Ga-FAPI PET/CT in primary staging of breast cancer in comparison with 18F-FDG PET/CT. METHODS: In this prospective study, 50 breast cancer patients (49F,1M, age:54.56 ± 13.73) were included. 18F-FDG PET/CT and 68Ga-FAPI PET/CT were performed consecutively for staging purposes. Patient-based sensitivity, specificity, PPV, NPV and accuracy were calculated. Relationship between semiquantitative 68Ga-FAPI PET parameters and histopathology were analysed. RESULTS: Patient based sensitivity for detection of primary breast lesions of 68Ga-FAPI were higher than 18F-FDG PET/CT (100 % (95 % CI: 92.9-100.0) vs 92 % (95 % CI: 80.4-100)), although not reached statistical significance (exact McNemar p = 0.0625). PPV was 100 % (95 % CI: 92.9-100.0) for both modalities. For lymph node metastases, patient-based sensitivity, specificity, PPV, NPV and accuracy of 68 Ga-FAPI PET/CT were 72.4 % (95 % CI: 52.8-87.3), 95.2 % (95 % CI: 76.2-99.9), 95.5 % (95 % CI: 77.2-99.9), 71.4 % (95 % CI: 51.3-86.8) and 82.0 % (95 % CI: 68.6-91.4), respectively, whereas those of 18F-FDG PET/CT were 60.7 % (95 % CI: 40.6-78.5), 85.7 % (95 % CI: 63.7-97.0), 85.0 % (95 % CI: 62.1-96.8), 62.1 % (95 % CI: 42.3-79.3) and 71.4 % (95 % CI: 56.7-83.4), respectively (for sensitivity and specificity, exact McNemar p = 0.125 and p = 0.50). Mean SUVmax of 68Ga FAPI uptake of primary breast lesions were significantly higher than 18F-FDG uptake (13.32 ± 7.1 vs 6.86 ± 3.51p < 0.001). Ki-67 of the primary tumors was correlated with SUVmean and TLU of axillary lymph nodes (r = 0.64,p = 0.006 and r = 0.66,p = 0.004). PR positivity and TV of the breast lesions were inversely correlated (r = -0.32,p = 0.044). There were 4 patients with distant metastasis: skeletal metastases in 3 patients and liver metastasis in one patient. 68Ga-FAPI showed greater number of skeletal metastasis in 1 patient and revealed an 18F-FDG negative liver metastasis in another patient. 68Ga-FAPI PET/CT changed management in 6 patients (12 %). Exploratory subgroup analyses demonstrated that 68Ga-FAPI PET/CT maintained a 100 % detection rate across all evaluated biological subgroups, whereas the detectability of 18F-FDG PET/CT varied according to tumor biology, with the lowest detection rate observed in Grade 1 tumors; paired subgroup comparisons using the exact McNemar test did not demonstrate statistically significant differences in detectability rates, although 68Ga-FAPI PET/CT showed significantly higher SUVmax values in several biological subgroups, particularly in hormone receptor-positive and Grade 1 tumors. CONCLUSION: 68Ga-FAPI PET/CT demonstrated promising diagnostic performance for the detection of primary breast tumors, lymph node metastases, and selected distant metastatic lesions. Although paired statistical analysis did not demonstrate significant differences compared with 18F-FDG PET/CT, 68Ga-FAPI PET/CT provided additional clinically relevant findings in a subset of patients. Larger multicenter studies are needed to further define its clinical role in breast cancer staging.