Potential improvement in the diagnostic accuracy in detecting the estrogen receptor status in metastatic and recurrent breast cancer using 18F-FES PET/CT in the US.

• DOI: 10.1200/jco.2023.41.16_suppl.3063
• Publication Date: 2023-06-04T15:23:35Z
• Authors: Adolfo Fuentes-Al...; Nicholas DiGregorio; Kurt Neeser; Jiran Jin; Regina Young
• Keywords: 03 medical and health sciences; 0302 clinical medicine; 3. Good health

3063 Background: ER status helps classify BC for the most appropriate treatment pathway. Biopsy (Bx) and immunohistochemical (IHC) are established procedures to determine the ER status in metastatic BC (mBC, i.e., first occurrence of metastases) and recurrent BC (rBC, i.e., progression of mBC). In some cases, the accuracy of Bx/IHC to inform ER status may be challenged (e.g. difficult to access lesions; ER discordance within/across lesions and due to temporal heterogeneity; and when a Bx fails to obtain representative tissue). 16α-18F-fluoro-17β-fluoroestradiol (18F-FES) is a radiolabeled form of estrogen that binds to ER. For use with positron emission tomography /computed tomography imaging (PET/CT), it allows an assessment of whole-body ER+ status. In prospective trials and meta-analyses, 18F-FES PET/CT provided high diagnostic accuracy (DA) of ER+ disease. This study evaluated the potential increase in accuracy in determining ER+ status when 18F-FES PET/CT was added to IHC in mBC and rBC. Methods: An Excel based decision model was developed to estimate the impact on DA for ER+/HER2- US mBC and rBC patients over a five-year period by introducing 18F-FES PET/CT. The model assumed that 18F-FES PET/CT was added to Bx/IHC to classify ER status in three cases: (i) for mBC patients when Bx failed or was inconclusive, (ii) for mBC patients when Bx was not possible, or (iii) for all rBC patients. The DA between two scenarios was compared: scenario A, DA of Bx/IHC only and scenario B, 18F-FES PET/CT + Bx/IHC. Results: Scenario B, adding 18F-FES PET/CT, may lead to an increase in the initiation of appropriate endocrine- and chemotherapies, as defined by clinical practice guidelines, in all comparisons. The largest increase in DA was in rBC and, when BX is not possible, in mBC patients. Also, results indicate that introducing 18F-FES PET/CT decreases the number of re-biopsies performed except when Bx was not possible (ii). Conclusions: Adding 18F-FES PET/CT to Bx/IHC is expected to improve the DA of a patients’ ER status thereby increasing the information available to inform treatment, thus reducing the need for re-biopsies in mBC and rBC patients. By far the largest increase in DA of ER status using 18F-FES PET/CT was seen among patients with rBC (iii). [Table: see text]