FES-PET and breast carcinomas: Current situation in 2021

In theory, FES has characteristics that are quite ideal for molecular imaging of receptors. It is a specific tracer, the uptake of which is well correlated with the expression of ER, labeled with fluorine-18, allowing relatively easy distribution to nuclear medicine departments for a common pathology, with a good tumor-to-background ratio, making it possible to establish a mapping of ER-positive (ER+) lesions and, thus, to highlight an inter-metastatic heterogeneity based on the combination of FDG and FES. The heterogeneity in this case corresponds to the concomitance of metastatic FES/FES+ lesions. On the other hand, the hepatobiliary elimination of FES does not allow the detection of ER+ liver metastases, nor a precise analysis of the abdominal cavity. In addition, the results established from studies with insufficient levels of evidence, this situation being partly linked to its lack of availability, did not allow the development of FES-PET imaging in clinical practice. The lack of sensitivity and specificity to predict a tumor response to hormone therapy, which is now often associated with therapy targeting signaling pathways 'parallel' to ER, represent other limits to its prescription by oncologists. Its sale since March 2017 in France and since early 2021 in the USA and its reimbursement since 2020 in France could at least make it possible to perform FES-PET imaging in patients with initially ER+ metastatic breast cancer or early recurrence after hormone therapy, to map the ER+ lesions when the biopsy is deemed impossible and another line of hormone therapy is considered. Another situation to investigate is that of mammary carcinomas with low metabolic activity, such as infiltrating lobular carcinomas, or in clinical dilemma, in particular in case of equivocal lesions on conventional work-up. (authors)