Impact of¹⁸F-FES PET/CT on Clinical Decisions in the Management of Recurrent or Metastatic Breast Cancer

The clinical impact of 16α-¹⁸F-fluoro-17β-estradiol (¹⁸F-FES) PET/CT on patient management has not been well investigated. The aim of this study was to assess the clinical impact of ¹⁸F-FES PET/CT on the management of patients with recurrent or metastatic breast cancer. <b>Methods:</b> Study subjects were identified retrospectively from a database of a prospective trial for postmarketing surveillance of ¹⁸F-FES between 2021 and 2023. Patients who were suspected or known to have recurrent or metastatic estrogen receptor-positive breast cancer based on a routine standard workup were included. Planned management before and actual management after ¹⁸F-FES PET/CT were assessed by 2 experienced medical oncologists via medical chart review. A 5-point questionnaire was provided to evaluate the value of ¹⁸F-FES PET/CT for management planning. The rate of intention-to-treat and interdisciplinary changes, and the impact of ¹⁸F-FES PET/CT according to PET/CT result or clinical indication, were examined. <b>Results:</b> Of the 344 included patients, 120 (35%) experienced a change in management after ¹⁸F-FES PET/CT. In 139 (40%) patients,¹⁸F-FES PET/CT supported the existing management decision without a change in management. Intention-to-treat and interdisciplinary changes accounted for 64% (77/120) and 68% (82/120) of all changes, respectively. A higher rate of change was observed when lesions were ¹⁸F-FES-negative (44% [36/81]) than ¹⁸F-FES-positive (30% [51/172]) or mixed ¹⁸F-FES-positive/negative (36% [33/91]). Regarding clinical indications, the highest rate of change was shown when evaluating the origins of metastasis of double primary cancers (64% [9/14]). <b>Conclusion:</b> ¹⁸F-FES PET/CT modified the management of recurrent or metastatic breast cancer, serving as an impactful imaging modality in clinical practice.