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 18 F-FDG. The estrogen receptor (ER) is commonly expressed in ILCs, suggesting a potential benefit of targeting with the ER probe 18 F-FES in this patient population. The objective of this study was to evaluate the diagnostic performance of 18 F-FES imaging in patients with metastatic ILC and compare it with that of 18 F-FDG. Methods We conducted a retrospective analysis of 20 ILC patients who underwent concurrent 18 F-FES and 18 F-FDG PET/CT examinations in our center. 18 F-FES and 18 F-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 SUV max 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 18 F-FDG in nonbone lesions was higher than that of 18 F-FES (57 vs 37, P < 0.001). 18 F-FES demonstrated a superior ability to detect nonbone lesions in 4 patients, whereas 18 F-FDG was superior in 5 patients ( P > 0.05). Among 9/16 patients with bone metastasis, 18 F-FES demonstrated a significant advantage in the detection of bone lesions compared with 18 F-FDG ( P = 0.05). Furthermore, patients with only 18 F-FES–positive lesions (12/12) were administered endocrine regimens, whereas patients lacking 18 F-FES uptake (2/3) predominantly received chemotherapy. Conclusions 18 F-FES is more effective than 18 F-FDG in detecting bone metastasis in ILC, but it does not demonstrate a significant advantage in nonbone lesions. Additionally, the results of examination with 18 F-FES have the potential to guide patient treatment plans.