Metabolic changes in breast cancer on dual-time-point 18F-FDG PET/CT imaging according to primary tumor uptake and background parenchymal enhancement.

OBJECTIVE This study was aimed at investigating metabolic changes in breast cancer on dual-time-point 18F-FDG PET/CT imaging (DTPI) according to primary tumor uptake and determining whether this technique is affected by background parenchymal enhancement (BPE). METHODS A total of 189 patients with newly diagnosed breast cancer who underwent DTPI examination were retrospectively evaluated. DTPI was performed using a standard FDG/PET protocol followed by delayed image acquisition at 120 min after injection. Patients were divided into two groups according to primary tumor uptake as breast cancer with low maximum standard uptake value (SUVmax) (< 2.5) and high SUVmax (≥ 2.5). The maximal SUV of the primary breast tumor (T-SUVmax), contralateral breast parenchyma uptake (B-SUVmax) according to different BPE grades, tumor to background ratio (T/B-SUVmax), and their percentage changes between early and delayed images (retention index, RI) were calculated. RESULTS For primary tumor uptake, tumors with high SUV had a significant increase in mean T-SUVmax between early and delayed images (8.17 vs. 9.16, P < 0.001), and %RI T-SUVmax was 10.52%. Conversely, mean T-SUVmax did not change between early and delayed images for tumors with low SUV (1.96 vs. 1.94, P = 0.610), and %RI T-SUVmax was - 1.41%. The mean %RI B-SUVmax was - 12.43% for minimal BPE, - 14.19% for mild BPE, - 19.49% for moderate BPE, and - 21.25% for marked BPE grade, indicating that higher BPE grades undergo better washouts on delayed imaging (β = - 3.220, P < 0.001 for trend). The %RI T/B-SUVmax of both breast cancer groups with low SUV and high SUV was 18.86% and 32.47%, respectively. CONCLUSIONS Breast cancer with low SUV undergoes no significant change in SUV on DTPI; however, washing of background parenchymal activity was evident over time, resulting in significantly increased tumor contrast in delayed images, which leads to increased sensitivity. Breast parenchymal washout was more significant with increased BPE level. Therefore, DTPI is expected to be more useful for evaluating breast lesions in regions with marked BPE on MRI.