Head-to-Head Evaluation of 18F-FES and 18F-FDG PET/CT in Metastatic Invasive Lobular Breast Cancer

Invasive lobular carcinoma (ILC) demonstrates lower conspicuity on F-18-FDG PET than the more common invasive ductal carcinoma. Other molecular imaging methods may be needed for evaluation of this malignancy. As ILC is nearly always (95%) estrogen receptor (ER)-positive, ER-targeting PET tracers such as 16 alpha-F-18-fluoroestradiol (F-18-FES) may have value. We reviewed prospective trials at Memorial Sloan Kettering Cancer Center using F-18-FES PET/CT to evaluate metastatic ILC patients with synchronous F-18-FDG and F-18-FES PET/CT imaging, which allowed a head-to-head comparison of these 2 PET tracers. Methods: Six prospective clinical trials using F-18-FES PET/CT in patients with metastatic breast cancer were performed at Memorial Sloan Kettering Cancer Center from 2008 to 2019. These trials included 92 patients, of whom 14 (15%) were of ILC histology. Seven of 14 patients with ILC had F-18-FDG PET/CT performed within 5 wk of the research F-18-FES PET/CT and no intervening change in management. For these 7 patients, the F-18-FES and F-18-FDG PET/CT studies were analyzed to determine the total number of tracer-avid lesions, organ systems of involvement, and SUVmax of each organ system for both tracers. Results: In the 7 comparable pairs of scans, there were a total of 254 F-18-FES-avid lesions (SUVmax, 2.6-17.9) and 111 F-18-FDG-avid lesions (SUVmax, 3.3-9.9) suggestive of malignancy. For 5 of 7 (71%) ILC patients, F-18-FES PET/CT detected more metastatic lesions than F-18-FDG PET/CT. In the same 5 of 7 patients, the SUVmax of F-18-FES-avid lesions was greater than the SUVmax of F-18-FDG-avid lesions. One patient had F-18-FES-avid metastases with no corresponding F-18-FDG-avid metastases. There were no patients with F-18-FDG-avid distant metastases without F-18-FES-avid distant metastases, although in one patient liver metastases were evident on F-18-FDG but not on F-18-FES PET. Conclusion: F-18-FES PET/CT compared favorably with F-18-FDG PET/CT for detection of metastases in patients with metastatic ILC. Larger prospective trials of F-18-FES PET/CT in ILC should be considered to evaluate ER-targeted imaging for clinical value in patients with this histology of breast cancer.

Automated summary

For patients with invasive lobular carcinoma (ILC), F-18-FES PET/CT shows comparable detection of metastases to F-18-FDG PET/CT. In a study, it was found that F-18-FES PET/CT may be more effective at detecting metastatic lesions in ILC patients compared to F-18-FDG PET/CT.