Clinical correlations with ¹⁸FDG PET scan patterns in solid pseudopapillary tumors of the pancreas: Still a surgical enigma?

Background: There are limited numbers of PET studies of solid pseudopapillary tumors (SPT) of the pancreas. Materials and methods: We reviewed the medical records of 37 patients who underwent resection of pancreatic SPT and had been preoperatively evaluated by ¹⁸F-FDG PET or PET/CT scan. Immunohistochemical analysis of glucose transporter-1 (GLUT-1) and hexokinase II (HK-II) was performed. Results: SPT could be categorized into five types according to the morphologic characteristics observed in PET images. Type I (hot FDG uptake in the entire tumor portion) was the most frequent (13, 34.2%), followed by type IV (focal uptake, 12, 31.6%), II (focal defect, 8, 21.1%), III (multiple and geographic uptake, 3, 7.9%), and V (total defective type, 1, 2.6%). The SUV_max in the solid portion of the SPT was 5.3 ± 4.1. The clinical pattern of FDG uptake in SPT was not associated with histopathologic features suggesting malignant potential. The SUV_max of SPT followed a pattern according to pattern of FDG uptake (R² = 0.203, p = 0.055), and was significantly associated with adjusted tumor volume (p = 0.001). GLUT-1 was not expressed in SPT, and only eight patients (12.3%) showed mild to moderate expression of HK-II, which was associated with the clinical pattern of SPT in PET images (p < 0.05). Conclusion: SPT of the pancreas could be categorized according to the morphologic patterns observed in PET images. The clinical significance of FDG uptake, glucose metabolism, and clinical usefulness of PET scan in SPT need to be further investigated, and thus this tumor remains a surgical enigma.