Value of F-FES PET in Solving Clinical Dilemmas in Breast Cancer Patients: A Retrospective Study.

Breast cancer (BC) is a heterogeneous disease in which estrogen receptor (ER) expression plays an important role in most tumors. A clinical dilemma may arise when a metastasis biopsy to determine the ER status cannot be performed safely or when ER heterogeneity is suspected between tumor lesions. Whole-body ER imaging, such as 16α-F-fluoro-17β-estradiol (F-FES) PET, may have added value in these situations. However, the role of this imaging technique in routine clinical practice remains to be further determined. Therefore, we assessed whether the physician's remaining clinical dilemma after the standard workup was solved by the F-FES PET scan. This retrospective study included F-FES PET scans of patients who had (or were suspected to have) ER-positive metastatic BC and for whom a clinical dilemma remained after the standard workup. The scans were performed at the University Medical Center of Groningen between November 2009 and January 2019. We investigated whether the physician's clinical dilemma was solved, defined either as solving the clinical dilemma through the F-FES PET results or as basing a treatment decision directly on the F-FES PET results. In addition, the category of the clinical dilemma was reported, as well as the rate of F-FES-positive or -negative PET scans, and any correlation to the frequency of solved dilemmas was determined. One hundred F-FES PET scans were performed on 83 patients. The clinical dilemma categories were inability to determine the extent of metastatic disease or suspected metastatic disease with the standard workup ( = 52), unclear ER status of the tumor ( = 31), and inability to determine which primary tumor caused the metastases ( = 17). The dilemmas were solved by F-FES PET in 87 of 100 scans (87%). In 81 of 87 scans, a treatment decision was based directly on F-FES PET results (treatment change, 51 scans; continuance, 30 scans). The frequency of solved dilemmas was not related to the clinical dilemma category ( = 0.334). However, the frequency of solved dilemmas was related to whether scans were F-FES-positive ( = 63) or F-FES-negative ( = 37; < 0.001). For various indications, the F-FES PET scan can help to solve most clinical dilemmas that may remain after the standard workup. Therefore, the F-FES PET scan has added value in BC patients who present the physician with a clinical dilemma.