FES PET (oestrogen receptor imaging)

What it measures. 18F-fluoroestradiol is oestradiol carrying a positron-emitting fluorine atom. Injected into a vein, it binds oestrogen receptors wherever they are expressed, and a PET scan maps that binding. A tumour that lights up is receptor positive; one that is dark either never had the receptor or has lost it, which happens in a quarter or more of metastases from an originally receptor-positive breast cancer.

Who should have it. The FDA approved 18F-fluoroestradiol (Cerianna, developed by Zionexa and now sold by GE HealthCare) in May 2020 as an adjunct to biopsy in patients with recurrent or metastatic breast cancer, to detect oestrogen receptor positive lesions. The Society of Nuclear Medicine and Molecular Imaging's appropriate use criteria list it as appropriate when biopsy is not feasible or lesions are discordant, when deciding whether to continue endocrine therapy after progression, and in lobular and other cancers that FDG PET images poorly. It is not a screening or staging test and it is uninformative in a patient taking a drug that blocks the receptor, such as fulvestrant, unless that drug has been paused.

What changes. A uniformly bright scan supports endocrine therapy or a hormone-based combination; dark lesions steer towards chemotherapy or an antibody-drug conjugate for those sites, and a mixed picture explains why a patient is progressing at one site on a treatment that works elsewhere. The tracer is made in regional cyclotron facilities and shipped, so availability follows the PET tracer network; the scan is priced like other specialist PET studies and is covered in the United States for the approved indication. In Europe it is available at a small number of centres under national rules.