Abstract
1701
Objectives To assess the in vivo uptake and tumor-to-noise ratio (T/N) of 4-fluoro-11β-methoxy-16α-[18F]-fluoroestradiol (4F-MFES) compared to 16α-[18F]-fluoroestradiol (FES), in estrogen receptor positive (ER+) and ERα knock-down (ERαKD) murine breast tumors.
Methods MC7-L1 and MC4-L2 mouse mammary adenocarcinoma cell lines (ER+) and their shRNA-carrying ERαKD equivalents were implanted subcutaneously in Balb/c mice. Mice were scanned 21 days later with either 10.5 MBq 4F-MFES or 4.5 MBq FES using a LabPET small animal scanner. The images were reconstructed using 20 MLEM iterations. After each scan sequence, a cylindrical phantom was used to obtain a calibration factor from which the percent injected dose per gram of tissue (%ID/g) data were derived. T/N values were obtained using the max 2×2 voxel cluster within tumor ROIs, divided by the average signal in a reference tissue ROI.
Results Both ER+ tumors had a significantly higher uptake of 4F-MFES and FES than their ERαKD equivalent (p < 0.01). Whereas there was a trend for higher %ID/g and T/N with 4F-MFES than FES in ERαKD tumors, ER+ tumor uptake of 4F-MFES was significantly higher (p < 0.05) even with the small sample investigated up to now (n=3). Accordingly, T/N was clearly higher for 4F-MFES than for FES in ER+ tumors (p < 0.05). 4F-MFES images also provided lower background and higher ER+ tumor contrast, hence improving the overall image quality.
Conclusions Our data suggest that the estrogenic tracer 4F-MFES may have a better potential for detecting breast lesions with borderline ER positivity in the clinical setting since higher tumor uptake and better contrast can be achieved than with the FES gold standard