Purpose: The aim of this study was to assess whether the retention index (RI) determined using dual-phase 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) reflects the malignant features of breast cancer.
Methods: A total of 1,523 patients with breast cancer were retrospectively evaluated. PET/CT scans were performed at 1 h and 2 h after FDG administration before treatment. The maximum standardized uptake value (SUVmax) at both time points (SUVmax1 and SUVmax2) in the primary tumour and RI were calculated. Primary tumour tissues were evaluated in terms of biological features, such as histology, nuclear grade, lymphovascular invasion and molecular subtype.
Results: Of the 1,523 patients, 463 (30.4%) had luminal A-like, 661 (43.4%) had luminal B-like, 229 (15.0%) had human epidermal growth factor receptor 2-positive (HER2-positive), and 157 (10.3%) triple-negative breast cancer. The median SUVmax1, SUVmax2 and RI values were 2.2, 2.3 and 2.6%, respectively. These metabolic parameters were correlated with tumour size, nodal metastasis, histology, nuclear grade, lymphovascular invasion, and molecular subtype (all P < 0.001). The median RI values were 0% in luminal A-like, 5.3% in luminal B-like, 6.9% in HER2-positive, and 11.4% in triple-negative breast cancer. RI was associated with malignant features when the tumour accumulated a significant amount of FDG. In a subanalysis of patients with tumours of stages T2 to T4, RI was correlated with nodal metastasis, histology, nuclear grade, and molecular subtype (luminal A-like 4.8%, luminal B-like 12.3%, HER2-positive 15.8%, and triple-negative 16.3%).
Conclusion: RI determined using delayed-phase FDG PET/CT is associated with malignant features in breast cancers with significant FDG uptake. Dual-phase imaging was helpful in distinguishing luminal A-like breast cancer from luminal B-like, HER2-positive, and triple-negative breast cancers.
Keywords: Breast cancer; Dual-phase; FDG; PET; Retention index.