Marginally calcified totally necrotic tumor of the pancreas: a subset of solid pseudopapillary tumor with near-total necrosis?

Metabolic characteristics of solid pseudopapillary neoplasms of the pancreas: their relationships with high intensity 18F-FDG PET images

Objective

We aimed to investigate the metabolic characteristics of Solid pseudopapillary neoplasms (SPNs) in relation signal intensities on ¹⁸F-FDG PET scans.

Summary Background Data

SPNs of the pancreas commonly show high uptake of 18F-FDG. However, the metabolic characteristics underlying the high ¹⁸F-FDG uptake in SPNs are not well characterized.

Materials and Methods

mRNA expressions for glucose metabolism were analyzed in five SPNs, five pancreatic ductal adenocarcinomas (PCAs), and paired normal pancreatic tissues. Among the proteins involved in glucose metabolism, the expressions of five proteins (GLUT1, HK1, PFKM, ENO2, and PKM2) were evaluated in 36 SPNs by immunohistochemistry. Clinical patterns of SPN on PET scans were classified according to the proportion of ¹⁸F-FDG uptake within the whole tumor volume (hot: ≥ 70%, mixed: 30 ≤ < 70, and defective: < 30%). PET-based parameters, including maximum standardized uptake value (SUV_max) and metabolic tumor volume (TMV_2.5), were evaluated.

Results

Hot (n = 19), mixed (n = 5), and defective (n = 12) ¹⁸F-FDG uptake patterns were noted in the 36 patients. Radiologic tumor size and SUV_max differed significantly according to these patterns (ANOVA, p < 0.05). GLUT1, HK1, PFKM, ENO2, and PKM2 were highly expressed in SPNs at both the mRNA and protein levels. Defective type SPNs showed lower expression of HK1 (p = 0.014), PKM2 (p = 0.028), and Ki-67 (p = 0.070) with frequent intra-tumoral necrosis (p = 0.007). High Ki-67 expression (≥ 3%) was associated with high SUV_max in pancreatic SPNs (p = 0.002).

Conclusions

SPN cells harbor an active molecular capacity for increased glucose metabolism. Especially, defective type SPNs were associated with low metabolic activity and related to low Ki-67 index.

Clinical correlations with (18)FDG 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 (18)F-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 SUVmax 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 SUVmax of SPT followed a pattern according to pattern of FDG uptake (R(2) = 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.