The estrogen receptor α (ERα) is expressed in approximately 70% of ovarian cancer tumors. PET of tumor ERα expression with the tracer 16α-(18)F-fluoro-17β-estradiol ((18)F-FES) may be valuable to select ovarian cancer patients for endocrine therapy. The aim of this study was to evaluate the feasibility of (18)F-FES PET to determine tumor ERα expression noninvasively in epithelial ovarian cancer patients.
Methods: (18)F-FES PET/CT was performed shortly before cytoreductive surgery. Tumor (18)F-FES uptake was quantified for all lesions 10 mm or greater on CT and expressed as maximum standardized uptake value. (18)F-FES PET/CT findings were compared with histology and immunohistochemistry for ERα, ERβ, and progesterone receptor. Receptor expression was scored semiquantitatively using H-scores (percentage of positive tumor cells × staining intensity). The optimum threshold to discriminate ER-positive and -negative lesions was determined by receiver-operating-characteristic analysis.
Results: In the 15 included patients with suspected ovarian cancer, 32 measurable lesions greater than 10 mm were present on CT. Tumor (18)F-FES uptake could be quantified for 28 lesions (88%), and 4 lesions were visible but nonquantifiable because of high uptake in adjacent tissue. During surgery, histology was obtained of 23 of 28 quantified lesions (82%). Quantitative (18)F-FES uptake correlated with the semiquantitative immunoscore for ERα (ρ = 0.65, P < 0.01) and weakly with progesterone receptor expression (ρ = 0.46, P = 0.03) and was not associated with ERβ expression (ρ = 0.21, P = 0.33). The optimum threshold to discriminate ERα-positive and ERα-negative lesions was a maximum standardized uptake value greater than 1.8, which provided a 79% sensitivity, 100% specificity, and area under the curve of 0.86 (95% confidence interval, 0.70-1.00). In 2 of 7 patients with cytology/histology available at primary diagnosis and at debulking surgery, immunohistochemical ERα expression had changed over time. (18)F-FES PET was in accordance with histology at debulking surgery but not at primary diagnosis, indicating that (18)F-FES PET could provide reliable information about current tumor ERα status.
Conclusion: (18)F-FES PET/CT can reliably assess ERα status in epithelial ovarian cancer tumors and metastases noninvasively. Evaluation of the predictive value of (18)F-FES PET/CT for endocrine therapy in epithelial ovarian cancer patients is warranted.
Keywords: FES PET; estrogen receptor; imaging; ovarian cancer.
© 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.