*Review* **Head-to-Head Comparison between 18F-FES PET/CT and 18F-FDG PET/CT in Oestrogen Receptor-Positive Breast Cancer: A Systematic Review and Meta-Analysis**

**Arnoldo Piccardo 1,\*, Francesco Fiz 1, Giorgio Treglia 2,3,4, Gianluca Bottoni 1,† and Pierpaolo Trimboli 2,5,†**


**Abstract:** 18F-FDG PET/CT is a powerful diagnostic tool in breast cancer (BC). However, it might have a reduced sensitivity in differentiated, oestrogen receptor-positive (ER+) BC. In this setting, specific molecular imaging with fluorine-oestradiol (18F-FES) PET/CT could help in overcoming these limitations; however, the literature on the diagnostic accuracy of this method is limited. We therefore planned this systematic review and meta-analysis to compare 18F-FDG and 18F-FES PET/CT in ER+ BC patients. We performed a literature search to identify all studies performing a head-tohead comparison between the two methods; we excluded review articles, preclinical studies, case reports and small case series. Finally, seven studies were identified (overall: 171 patients; range: 7–49 patients). A patients-based analysis (PBA) showed that 18F-FDG and 18F-FES PET/CT had a similar high pooled sensitivity (97% and 94%, respectively) at the lesion-based analysis (LBA), 18F-FES performed slightly better than 18F-FDG (pooled sensitivity: 95% vs. 85%, respectively). Moreover, when we considered only the studies dealing with the restaging setting (n = 3), this difference in sensitivity was even more marked (98% vs. 81%, respectively). In conclusion, both tracers feature an excellent sensitivity in ER+ BC; however, 18F-FES PET/CT could be preferred in the restaging setting.

**Keywords:** PET/CT; FDG; FES; breast cancer; oestrogen receptor; diagnosis; nuclear medicine
