Abstract 1415: Staging with [18F]FDG PET/CT
Authors: Iqbal Ramsha , Aras Tuba , Mammatas Lemonitsa , Vogel Wouter V. , Oprea-Lager Daniela E. , Verheul Hendrik M. , Boellaard Ronald , Oordt Catharina W. Menke-van der Houven van 
Published: August 2019

Abstract
Background: Accurate staging of patients with primary breast cancer is essential for an optimal treatment plan. The current imaging standard for staging, positron emission tomography/computed tomography with [18F]Fluorodeoxyglucose ([18F]FDG PET/CT), might be insufficient for detection of distant metastases, specifically in low grade, estrogen receptor positive (ER+) breast cancer, due to lower metabolic activity. The aim of this study was to investigate the efficacy of [18F]FDG PET/CT in staging patients with low-intermediate grade, ER+ breast cancer.
Methods: 79 patients diagnosed with grade 1-2, ER+ clinical stage IIB/III or locoregional recurrent breast cancer were retrospectively included. Visual analysis was performed, comparing the lesions detected on conventional imaging modalities (mammography, ultrasound, magnetic resonance imaging, computed tomography, bone scintigraphy) with lesions detected on [18F]FDG PET/CT. Conventional imaging and/or pathology outcomes were considered as the gold standard for this comparison. Tracer uptake in each PET-positive lesion was (semi)quantified: volumes of interest were defined on the PET scan to determine standardized uptake values (SUVmax, SUVmean, SUVpeak), total lesion glycolysis (TLG) and metabolic tumor volume (MTV). These quantitative parameters were correlated with pathological features of tumors (i.e. histological subtype, grade, ER/PR/HER2 expression and mitotic activity index) to assess whether tracer uptake is influenced by these features.
Results: Scans were analyzed visually and (semi)quantitatively. 370 lesions could be identified with all imaging modalities (primary lesions: 80, locoregional lymph nodes: 161, distant lesions: 129). Based on the gold standard, 226/370 (61.1%) lesions were interpreted as “true positive” on [18F]FDG PET, 134/370 (36.2%) as “false positive” and 10/370 (2.7%) as “false negative” on [18F]FDG PET (p = 0.016). “False positive” lesions were mainly located in the axilla region (e.g. reactive lesions), gynecological and gastro-intestinal tract (e.g. adenomas) whereas “false negative” lesions were predominantly located in osseous tissue. The average SUVmax for “true positive” and “false positive” lesions was 4.24 ± 2.97 and 3.96 ± 2.03, respectively. For “true positive” lesions SUVmax, SUVpeak, SUVmean and MTV correlated with histological subtype, showing higher uptake in ductal carcinoma compared to lobular carcinoma (p &lt;0.023). SUVmax and SUVmean also correlated with PR expression (p &lt;0.034). No other correlations could be found between quantitative parameters and pathology outcomes.
Conclusion: These preliminary data indicate that [18F]DGG PET/CT might not correctly identify a substantial amount of lesions and therefore could lead to incorrect staging of patients with low grade, ER+ breast cancer. This suggests that there is a need to improve current staging procedures.
Citation Format: Ramsha Iqbal, Tuba Aras, Lemonitsa Mammatas, Wouter V. Vogel, Daniela E. Oprea-Lager, Hendrik M. Verheul, Ronald Boellaard, Catharina W. Menke-van der Houven van Oordt. Staging with [18F]FDG PET/CT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1415.