Annals of nuclear medicine

Lesion-based analysis of (18)F-FDG uptake and (111)In-Pentetreotide uptake by neuroendocrine tumors.

PMID 25179521


To characterize the heterogeneity of metastatic neuroendocrine tumor (NET) lesions, we compared the [(18)F]-fluorodeoxyglucose (FDG) uptake and the (111)In-pentetreotide (SRS) uptake for somatostatin receptor scintigraphy using the CT-based fusion imaging techniques of PET/CT and SPECT/CT. Fifteen consecutive patients with NET lesions were examined using both FDG-PET/CT and SRS SPECT/CT prospectively. A total of 45 metastatic NET lesions were evaluated for FDG uptake according to the standardized uptake value (SUV) and for SRS uptake according to the tumor-to-muscle count ratio (T/M ratio); these values were then compared according to the grade of NET (G), also compared to the tumor volume. Both the SRS uptake and FDG uptake showed no significant correlation to the tumor volume, and suggested no significant artifacts in these data. The T/M ratio for the SRS uptake ranged from 192.7 to 1.9 and exhibited very wide range of distribution. The SUV for the FDG uptake ranged from 13.8 to 0.77 and exhibited narrow range of distribution. The uptake of the two tracers in individual lesions showed an inverse correlation. The G1xa0+xa02 lesions had a higher SRS uptake than the G3 lesions, but the difference was not significant because of the large variation (40.65xa0±xa048.03, nxa0=xa039 vs. 8.66xa0±xa013.13, nxa0=xa06). However, the G1xa0+xa02 lesions had a significantly lower FDG uptake than the G3 lesions (3.52xa0±xa01.84, nxa0=xa039 vs. 10.82xa0±xa04.50, nxa0=xa06). The tracer uptakes varied largely not only in an inter-subject manner, but also in an intra-subject manner. An inverse correlation between SRS uptake and FDG uptake in the metastatic NET lesions observed in this study may be consistent with the opposing ideas of differentiation and proliferation in oncology. The large variations in SRS and FDG uptake by metastatic NET lesions suggest the biological heterogeneity of advanced NET. These results support the idea that combination therapy targeting both receptor-positive cells and proliferating cells may be beneficial from a functional imaging perspective.