[18F]Fluoroestradiol Uptake in Benign Nodular Sclerosing Adenosis of the Breast

A 70-year-old woman with estrogen receptor-positive (ER+) invasive ductal carcinoma (IDC) of the right breast underwent 18F-fluoroestradiol (18F-FES) PET/CT demonstrating uptake in the IDC (SUVmax 2.5) and also extensive 18F-FES uptake in bilateral breasts corresponding to marked bilateral background enhancement on MRI. MRI-guided biopsy of a representative enhancing 18F-FES-avid region in the left breast (SUVmax 3.5) revealed nodular sclerosing adenosis without cellular atypia or malignancy, but with 30% ER positivity on immunohistochemistry. False-positive uptake of 18F-FES is reported in irradiated lung and interstitial lung disease. This case highlights another mechanism of false-positive 18F-FES uptake due to ER overexpression in benign breast tissue.