Can ¹⁸F-FES PET Improve the Evaluation of ¹⁸F-FDG PET in Patients With Metastatic Invasive Lobular Carcinoma?

Purpose : Invasive lobular carcinoma (ILC) exhibits a low affinity for F-18-FDG. The estrogen receptor (ER) is commonly expressed in ILCs, suggesting a potential benefit of targeting with the ER probe F-18-FES in this patient population. The objective of this study was to evaluate the diagnostic performance of F-18-FES imaging in patients with metastatic ILC and compare it with that of F-18-FDG. Methods : We conducted a retrospective analysis of 20 ILC patients who underwent concurrent F-18-FES and F-18-FDG PET/CT examinations in our center. F-18-FES and F-18-FDG imaging were analyzed to determine the total count of tracer-avid lesions in nonbone sites and their corresponding organ systems, assess the extent of anatomical regions involved in bone metastases, and measure the SUVmax values for both tracers. Results : Among 20 ILC patients, 65 nonbone lesions were found to be distributed in 13 patients, and 16 patients were diagnosed with bone metastasis, which was distributed in 54 skeletal anatomical regions. The detection rate of F-18-FDG in nonbone lesions was higher than that of F-18-FES (57 vs 37, P < 0.001). F-18-FES demonstrated a superior ability to detect nonbone lesions in 4 patients, whereas F-18-FDG was superior in 5 patients (P > 0.05). Among 9/16 patients with bone metastasis, F-18-FES demonstrated a significant advantage in the detection of bone lesions compared with F-18-FDG (P = 0.05). Furthermore, patients with only F-18-FES-positive lesions (12/12) were administered endocrine regimens, whereas patients lacking F-18-FES uptake (2/3) predominantly received chemotherapy. Conclusions : F-18-FES is more effective than F-18-FDG in detecting bone metastasis in ILC, but it does not demonstrate a significant advantage in nonbone lesions. Additionally, the results of examination with F-18-FES have the potential to guide patient treatment plans.