How FES PET Could Guide SBRT Selection in Metastatic Breast Cancer

In an interview with Pharmacy Times, Jose Bazan, MD, who leads the Breast Radiation Oncology program at City of Hope, discusses how FES PET imaging could improve patient selection for stereotactic body radiation therapy (SBRT) in oligoprogressive estrogen receptor (ER)-positive metastatic breast cancer.

Bazan explains that conventional imaging may not fully capture the extent of disease, potentially limiting clinicians’ ability to identify patients whose progression is confined to a few lesions. His ongoing phase 2 trial incorporates FES PET before radiation and during follow-up to assess ER-expressing disease alongside routine imaging.

Although the imaging questionnaires have not been fully analyzed, Bazan describes instances in which FES PET identified additional lesions that changed treatment decisions. Some patients initially considered eligible did not proceed to radiation, while others remained eligible but required additional lesions to be targeted. The scans also revealed lesions visible on conventional imaging that lacked FES uptake, raising questions about their estrogen receptor activity.

Bazan emphasizes that the preliminary systemic therapy findings require cautious interpretation. Half of the first eight patients remained on their current treatment for at least six months, but better selection methods are needed to distinguish limited progression from broader disease resistance. The study also collects circulating tumor DNA to investigate whether blood-based information can complement imaging.

For oncology pharmacists, Bazan highlights the importance of coordinating medication decisions with medical and radiation oncologists. Evidence regarding concurrent SBRT varies by systemic agent and treatment location, leaving uncertainty around some CDK4/6 inhibitors and newer oral selective estrogen receptor degraders.

He also stresses medication review before FES PET. Therapies that bind to or alter estrogen receptors can interfere with imaging interpretation, making advance planning essential. Pharmacists can help identify these medications and coordinate any required washout with the treatment team while protecting continuity of cancer care.