Quantitative FES-PET can predict response to hormonal therapy and may help guide treatment selection. Treatment selection using quantitative FES-PET in our patient series would have increased the rate of response from 23% to 34% overall, and from 29% to 46% in the subset of patients lacking HER2/neu overexpression. A multi-institutional collaborative trial would permit definitive assessment of the value of FES-PET for therapeutic decision making.

The PET compound 18 F-fluoroestradiol ( 18 F-FES) has been developed and tested as an agent for the imaging of estrogen receptor (ER) expression in vivo. 18 F-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 18 F-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 18 F-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 18 F-FES uptake were compared with ER expression measured by 3 different ER scoring methods: qualitative scoring (0-31), the Allred score (0-10), and a computerized IHC index. Results: There was excellent agreement (r 5 0.99) between observers using IHC as well as the different methods of measuring ER content (P , 0.001). ER-negative tumors had 18 F-FES partial-volumecorrected 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 18 F-FES uptake ranged from 0.57 to 0.73, with the best correlation being between the computerized IHC index and 18 F-FES partial-volume-corrected standardized uptake values. Conclusion: Our results showed good agreement between 18 F-FES PET and ER expression measured by IHC. 18 F-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.

LABC patients with limited or no decline in BF and FDG K(1) experienced higher recurrence and mortality risks that were greater than the effects of clinical tumor characteristics. Tumor perfusion changes over the course of neoadjuvant chemotherapy measured directly by [(15)O]water or indirectly by dynamic FDG predict DFS and OS.