Comparative study between 18-F FDG PET/CT and 18-F FES PET/CT in estrogen receptor positive breast cancer patients

Purpose: 16a-[ ¹⁸ F]fluoro-17b-estradiol (FES) is a promising synthetic estrogen analogue which when used as tracer for PET scan, provides an in vivo estimate of tumor estrogen receptor (ER) status in breast cancer. This study aims to investigate the diagnostic accuracy of FES PET scan in diagnosing ER positive lesions in breast cancer patients. Method: In this single centre prospective study, 57 ER positive breast cancer patients underwent both FDG PET and FES PET during the study period of two years. The number of lesions suspected for disease by either modality were calculated and their sensitivities were compared. Results 251 lesions were identified using FDG PET/CT and FES PET/CT; eight were proven to be true negatives by biopsy and were excluded. FDG PET had better sensitivity for detecting lesions, both overall (80.25% vs 61.32%, p  < 0.001) as well as non hepatic (80.08% vs 63.14%, p  < 0.001). However, FES PET exclusively identified 48 lesions and also helped characterize 18 FDG-PET positive lesions. Hence 18F-FES had an incremental value in 66 out of the 236 non-hepatic lesions (27.9%) either by characterizing 18-F FDG positive lesions or by exclusive detection of lesions not identified by 18-F FDG PET and resulted in change of management of 21.05% of patients. Conclusion 18-F FDG PET displays overall better sensitivity for detecting lesions. However, the value of 18-F FES PET lies in the exclusive lesions it identified and the number of FDG avid lesions it helped characterize, both by its negative as well as positive findings.