*4.4. Scientific Implications*

Imaging with FDG PET for patients with grade 1–2, ER + BC can potentially lead to incorrect staging. In the search for alternative methods to improve staging, imaging based on the ER, which is independent of metabolic activity, might be of interest. Several clinical studies have shown that 16 α-[18F]-fluoro-17β-estradiol ([18F]FES) PET/CT has overall high sensitivity (82–84%) and specificity (93–98%) rates [41], making it an interesting ER-targeting PET tracer to compare with FDG for the staging of patients with grade 1–2, ER + BC.
