LAUSR

Background: Bone dominant metastatic breast cancer can be difficult to stage using conventional imaging. 18F-FES is an estrogen analogue PET imaging tracer that measures estrogen receptor (ER) expression at multiple tumor sites simultaneously and predicts response to endocrine therapy. We analyzed FES-PET and FDG-PET SUV uptake within bone in patients with metastatic lobular breast cancer from an ER+ primary. Methods: We retrospectively reviewed FES and FDG SUV uptake from scans in women with boney lesions or diffuse marrow uptake (n = 30). Our cohort was obtained from various cross-sectional studies at our institution and the majority received multiple lines of prior endocrine and/or chemotherapy. Up to 10 lesions in each patient were evaluated for a total of 200 lesions in both FES and FDG images. Diffuse marrow uptake was found in 7 women, and we compared this subgroup (bone marrow) vs the others by two-sample t-test for FES/FDG scans. Progression free survival (PFS), from time of earliest scan date to progression or death (whichever came first), and overall survival (OS), from time of earliest scan date to death, was evaluated using Kaplan-Meier curves and the Log-Rank test. Results: Mean (range) SUVmax in FES and FDG respectively for all bone lesions were 3.9 (1.5-9.1) and 4.7 (1.4-9.5). Higher FES and FDG uptake were noted in patients with bone marrow uptake (mean FES SUVmax 5.2 and mean FDG SUVmax 5.7) compared to non-marrow bone uptake (mean FES SUVmax 3.5 and mean FDG SUVmax 4.4), and the average difference for FES SUVmax was statistically significant higher in bone marrow uptake subgroup (p=0.032). Of the 200 lesions identified, 92 (46%) were located in the spine. Bone marrow uptake was visually more pronounced in the FES-PET scans. Compared to bone only uptake, patients with bone marrow uptake had a higher progression free survival (1.3 years vs 0.57 years p = 0.12), but similar overall survival (1.56 years vs 1.63 years, p = 0.69). Conclusions: Amongst patients with metastatic lobular carcinoma involving the bone marrow, there was significant higher uptake in both FES and FDG scans which provides insight in the pattern of spread of lobular breast cancer. Metastatic bone dominant breast cancers have similar FES and FDG avidity, suggesting that both imaging modalities can be used in identification of bone tumor sites. Further prospective trials are needed to confirm the utility of FES to stage extent of disease in bone dominant metastatic lobular breast cancer. Citation Format: Poorni Manohar, Lanell Peterson, Qian (Vicky) Wu, Isaac Jenkins, Brenda Kurland, Alena Novakova-Jiresova, Jennifer Specht, Mark Muzi, Jeanne Link, Kenneth Krohn, Paul Kinahan, David Mankoff, Hannah Linden. The role of 18F-Fluoroestradiol (FES) and 18F-Fluorodeoxyglucose (FDG) PET imaging in identification of bone metastases in metastatic breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-01-07.