Concurrent inflammation or anemia at the time of PET/computed tomography (CT) could be one of several causes of diffuse splenic 18F-fluorodeoxyglucose (18F-FDG) uptake. In this study, we focused on cytokines to investigate interactions during this phenomenon and clarify the significance of splenic 18F-FDG uptake in PET/CT.
We selected 40 patients (17 women and 23 men) with cholangiocarcinoma, pancreatic cancer, or gallbladder cancer who had undergone PET/CT. These patients were subdivided into two groups (group A: patients showing splenic 18F-FDG uptake exceeding hepatic uptake; group B: patients showing hepatic 18F-FDG uptake exceeding splenic uptake). Blood sampling was performed for each patient on the same day as PET/CT, and 22 types of cytokines and hematologic indices were analyzed.
Group A showed higher levels of interleukin (IL)-1β (P=0.0478), IL-1RA (P=0.0044), IL-4 (P=0.0118), IL-6 (P=0.0375), IL-7 (P=0.0478), and IL-13 (P=0.0081) compared with group B. However, interferon-inducible protein-10 (IP-10; P=0.1714), IL-9 (P=0.8022), IL-8 (P=0.1631), IL-5 (P=0.5273), IL-3 (P=0.3097), IL-23 (P=0.1194), IL-2 (P=0.1099), IL-1α (P=0.4439), IL-17α (P=0.8811), IL-16 (P=0.3201), IL-15 (P=0.0580), interferon-γ (IFN-γ; P=0.5308), growth-regulated oncogene (GRO; P=0.2847), granulocyte macrophage-colony-stimulating factor (GM-CSF; P=0.0913), granulocyte-colony-stimulating factor (G-CSF; P=0.5244), and soluble CD40 ligand (sCD40L; P=0.1714) levels in group A were not statistically significantly different compared with those in the control group. In addition, the white blood cell counts and C-reactive protein levels in group A showed higher values compared with group B. IL-13 among the cytokines and C-reactive protein among the hematologic indices were significant predictors of splenic 18F-FDG uptake exceeding hepatic 18F-FDG uptake.
This study showed that splenic 18F-FDG uptake is related to IL-1β, IL-1receptor antagonist, IL-4, IL-6, IL-7, and IL-13. These cytokines may reflect the activation of humoral immunity of the spleen.