Utility of 18F-fluoroestradiol over 18F-fluorodeoxyglucose positron emission tomography/computed tomography in the initial diagnosis of over 90 metastatic lesions in a patient with metastatic estrogen receptor-positive breast cancer.

Approximately 6% of women with newly diagnosed breast cancer will present with metastatic disease. Proper staging workup and diagnosis of metastatic lesions is crucial prior to surgical treatment.¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is often included in the staging workup of locally advanced breast cancer. Recently, PET/CT with ¹⁸F-fluoroestradiol (¹⁸F-FES), a radiolabeled form of estradiol that binds to the estrogen receptor, has been approved as an additional imaging technique for the detection of estrogen receptor-positive lesions in patients with metastatic breast cancer. Though the two have been shown to have comparable sensitivity for diagnosis of metastatic lesions, there is still much debate regarding when to use ¹⁸F-FES PET/CT over ¹⁸F-FDG PET/CT imaging. We present the case of a 68-year-old patient diagnosed with estrogen and progesterone receptor-positive invasive ductal carcinoma of the left breast. Her staging workup included an ¹⁸F-FDG PET/CT that did not demonstrate any evidence of metastatic lesions. Due to discordant imaging findings, the patient then underwent ¹⁸F-FES PET/CT, which demonstrated over 90 metastatic osseous lesions. This study highlights the utility of ¹⁸F-FES PET/CT over ¹⁸F-FDG PET/CT in diagnosis of metastatic osseous lesions in a patient with metastatic estrogen receptor-positive breast cancer.