Head-to-Head Evaluation of <sup>18</sup>F-FES and <sup>18</sup>F-FDG PET/CT in Metastatic Invasive Lobular Breast Cancer
Gary A. Ulaner, Komal Jhaveri, Sarat Chandarlapaty, Vaios Hatzoglou, Christopher C. Riedl, Jason S. Lewis, Audrey Mauguen
Abstract
Invasive lobular carcinoma (ILC) demonstrates lower conspicuity on 18 F-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 16-18 F-fluoroestradiol ( 18 F-FES) may have value. We reviewed prospective trials at Memorial Sloan Kettering Cancer Center using 18 F-FES PET/CT to evaluate metastatic ILC patients with synchronous 18 F-FDG and 18 F-FES PET/CT imaging, which allowed a head-to-head comparison of these 2 PET tracers. Methods: Six prospective clinical trials using 18 F-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 18 F-FDG PET/CT performed within 5 wk of the research 18 F-FES PET/CT and no intervening change in management. For these 7 patients, the 18 F-FES and 18 F-FDG PET/CT studies were analyzed to determine the total number of tracer-avid lesions, organ systems of involvement, and SUV max of each organ system for both tracers. Results: In the 7 comparable pairs of scans, there were a total of 254 18 F-FES-avid lesions (SUV max , 2.6-17.9) and 111 18 F-FDG-avid lesions (SUV max , 3.3-9.9) suggestive of malignancy. For 5 of 7 (71%) ILC patients, 18 F-FES PET/CT detected more metastatic lesions than 18 F-FDG PET/CT. In the same 5 of 7 patients, the SUV max of 18 F-FES-avid lesions was greater than the SUV max of 18 F-FDG-avid lesions. One patient had 18 F-FES-avid metastases with no corresponding 18 F-FDG-avid metastases. There were no patients with 18 F-FDG-avid distant metastases without 18 F-FES-avid distant metastases, although in one patient liver metastases were evident on 18 F-FDG but not on 18 F-FES PET. Conclusion: 18 F-FES PET/CT compared favorably with 18 F-FDG PET/CT for detection of metastases in patients with metastatic ILC. Larger prospective trials of 18 F-FES PET/ CT in ILC should be considered to evaluate ER-targeted imaging for clinical value in patients with this histology of breast cancer.