Does Pet/Ct With 18f-Fluoroestradiol (18f-Fes) Contribute to the Assessment of Breast Cancer Compared to Fluorine-2-D-Deoxyglucose (18f-Fdg)?

While fluorine-2-D-deoxyglucose (18F-FDG) PET/CT is commonly used in the assessment of breast cancer, it has limitations, such as its inability to distinguish it from inflammatory and infectious conditions. In this context, another molecular imaging tool, PET/CT with 18F-fluoroestradiol (18F-FES), is emerging as a promising alternative. Preliminary data from the literature already shows comparable sensitivity between these exams in breast cancer with estrogen receptors. In addition, the latter seems relevant because it correlates with the concentration of these receptors, shows their expression non-invasively and suggests a theoretical gain in specificity. To evaluate whether 18F-FES PET/CT provides supplementary information to clinical reasoning when compared to 18F-FDG PET/CT in the assessment of breast cancer. A retrospective, observational, and comparative analysis was performed using information stored in the databases of a private institution regarding 18F-FES PET/CT scans performed in the context of breast cancer. The selection criteria required a complementary scan using 18F-FDG, which was met by thirteen out of the 14 tests found, however, one study was excluded from the analysis because its indication could not be precisely classified with the available data. The twelve selected tests were carried out between August 2022 and March 2024, on females with a mean age of 62.16 years. The time interval between studies using positron-emitting radioisotopes (18F-FES and 18F-FDG) ranged from 1 to 29 days. The administered activity of 18F-FES varied from 4.0 to 10.0 mCi, and the interval between administration and image acquisition ranged from 45 to 130 minutes. Among the findings showing 18F-fluoroestradiol uptake, breast lesions and thoracic lymph nodes were the most common, present in six and five reports, respectively. The indications for the scans varied, with ten intended for staging/restaging and two to address clinical uncertainty about the presence of estrogen receptors. In 40% of the staging/restaging subgroup, 18F-fluoroestradiol contributed to the clinical reasoning. 18F-FES showed uptake in lymph nodes without hypermetabolism and was able to provide diagnostic specificity, either by raising suspicion in a finding initially taken as benign or by predicting false-positive metabolic findings due to the absence of estrogen receptors. Regarding the evaluation of hormone receptor expression status, 18F-fluoroestradiol has supported a proposed change in the tumoral immunohistochemistry of a lesion non-invasively. 18F-FES PET/CT appears to provide additional relevant information in breast cancer, but future studies should evaluate the method's impact on clinical management.