Dr O’Brien on Advances in Molecular Imaging in ER+ Breast Cancer

Sophia R. O'Brien, MD, assistant professor, clinical radiology, Divisions of Nuclear Medicine and Breast Imaging, Perelman School of Medicine, co-director, TEACH Longitudinal Residency Track, Women in Radiology Group, University of Pennsylvania, discusses recent advances in the diagnosis and staging of estrogen receptor (ER)–positive metastatic breast cancer.

In 2020, the FDA approved fluorine 18 fluoroestradiol (FES) FES PET/CT imaging as an adjunct to biopsy for patients with recurrent or metastatic ER-positive breast cancer, O’Brien states.

This diagnostic procedure involves the use of a radioactive tracer that targets estrogen receptors in the nucleus of estrogen-expressing cells, O’Brien details. FES is often present in organs associated with high estrogen expression such as the uterus, organs involved in metabolism and excretion of the tracer, O’Brien adds. The radioactive tracer reveals the location of ER-expressing tumors at both the primary cancer site and the sites of metabolic disease, she explains.

Current guidelines recommend that sites of abnormal FES uptake should undergo a confirmatory biopsy. However, there are several limitations associated with this procedure in breast cancer, O’Brien continues. Up to 30% of metastatic sites for patients with ER expression in the primary tumor will be ER-negative, O’Brien says, adding that a confirmatory biopsy cannot be performed at each metastatic site to determine whether the hormone profiles are heterogenous. Additionally, serial biopsies are not performed while a patient is undergoing treatment, O’Brien notes. Any treatment-related changes leading to heterogeneity may accordingly remain undetected, she says.

Using FES PET/CT, a whole-body, in vivo assessment of disease can be conducted spatially or potentially serially over time, O’Brien states. This allows for improved selection of target lesions for confirmatory biopsies, assessment of ER expression heterogeneity, and increased understanding of tumor burden in functionally ER-positive metastatic breast cancer, O’Brien concludes.