Quantitative Imaging of Estrogen Receptor Expression in Breast Cancer with PET and ¹⁸F-Fluoroestradiol

¹ Department of Radiology, University of Washington/Seattle Cancer Care Alliance, Seattle, Washington
² Department of Pathology, University of Washington/Seattle Cancer Care Alliance, Seattle, Washington
³ Phenopath Laboratories, Seattle, Washington
⁴ Department of Nuclear Medicine, University of Iowa, Iowa City, Iowa

^* To whom correspondence should be addressed. E-mail: dam{at}u.washington.edu.

	Abstract

The PET compound ¹⁸F-fluoroestradiol (¹⁸F-FES) has been developed and tested as an agent for the imaging of estrogen receptor (ER) expression in vivo. ¹⁸F-FES uptake has been shown to correlate with ER expression assayed in vitro by radioligand binding; however, immunohistochemistry (IHC) rather than radioligand binding is used most often to measure ER expression in clinical practice. We therefore compared ¹⁸F-FES uptake with ER expression assayed in vitro by IHC with both qualitative and semiquantitative measures. Methods: Seventeen patients with primary or metastatic breast cancer were studied with dynamic ¹⁸F-FES PET; cancer tissue samples, collected close to the time of imaging, were assayed for ER expression by IHC. For each tumor, partial-volume-corrected measures of ¹⁸F-FES uptake were compared with ER expression measured by 3 different ER scoring methods: qualitative scoring (0–3+), the Allred score (0–10), and a computerized IHC index. Results: There was excellent agreement (r = 0.99) between observers using IHC as well as the different methods of measuring ER content (P < 0.001). ER-negative tumors had ¹⁸F-FES partial-volume-corrected standardized uptake values of less than 1.0, whereas ER-positive tumors had values above 1.1. Correlation coefficients for the different measures of ER content and the different measures of ¹⁸F-FES uptake ranged from 0.57 to 0.73, with the best correlation being between the computerized IHC index and ¹⁸F-FES partial-volume-corrected standardized uptake values. Conclusion: Our results showed good agreement between ¹⁸F-FES PET and ER expression measured by IHC. ¹⁸F-FES imaging may be a useful tool for aiding in the assessment of ER status, especially in patients with multiple tumors or for tumors that are difficult to biopsy.

Key Words: estrogen receptor, breast cancer, ¹⁸F-FES PET, IHC, tracer uptake

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