Study data presented at the 2019 San Antonio Breast Cancer Symposium suggest that 18F-fluoroestradiol (FES) and 18F-fluorodeoxyglucose (FDG) PET imaging can be used to identify bone metastases in patients with metastatic breast cancer.

Co-investigator Hannah M. Linden, MD, FACP, Athena Distinguished Breast Cancer Research Professor of Medicine, University of Washington, Seattle Cancer Care Alliance, spoke with Oncology Learning Network about the clinical significance of these results.

What existing data led you and your co-investigators to conduct this research?

We have been studying FES PET for many years as part of a program project grant in molecular imaging at the University of Washington. This is an imaging tracer which allows us to assay estrogen receptor (ER) function in metastatic breast cancer.

The ability of the metastatic tumor to concentrate estrogen is tested by this imaging modality. Tumors with the ability to bind and show ER function are likely sensitive to ER-directed (endocrine or “hormonal”) therapy.

Please briefly describe your study and its findings. What are the possible real-world applications of these results in clinical practice?

We found that FES shows activity in lobular breast cancers and can detect infiltrating lobular cancer in the bone and bone marrow, and that patients with marrow involvement did better than others—all of this is surprising.

FES PET is commercially available in Europe, and likely will become available in the United States. FES PET could be used to detect, diagnose, stage and help select appropriate treatment for patients, and will likely be useful for ductal and lobular metastatic breast cancer.

Used appropriately, this could have implications for precision medicine, getting the right patient the right drug, and even have cost savings.

Do you and your co-investigators intend to expand upon this research? If so, what are/will be your next steps?

We are working to study liquid biopsy versus imaging testing and are helping several companies evaluate ER blockade. There are many oral drugs, including selective ER down-modulators, which are likely to displace the intramuscular agent, fulvestrant. FES is helpful to show whether the candidate drugs are working.

Is there anything else pertaining to your research that you would like to add?

Patient specific testing helps to sort out whether the treatment is working in a given patient, working around any issues of bioavailablity.