Introduction:
The aim was to assess the diagnostic value of 99mTc-Tektrotyd scintigraphy (TCT) and positron emission tomography/computed tomography using F-18 fluorodeoxyglucose (18F-FDG PET/CT) in the detection and follow-up of neuroendocrine tumors (NETs), and their predictive value for disease progression.

Material and methods:
In this retrospective cohort, TCT and 18F-FDG PET/CT were performed in 90 patients (37 men, 53 women, mean age 52.7 ±15.1), with NET. Correlation of Ki67 and tumor grade versus Krenning score and SUVmax was assessed, Kaplan-Meier analysis was used for progression-free survival (PFS), and Cox regression analysis was performed to identify the association between progression-related factors and PFS.

Results:
Out of 90, true positive TCT was detected in 56 (62.2%) patients, true negative in 19 (21.1%), false positive in 4 (4.4%), false negative in 11 (12.2%), while 18F-FDG PET/CT was true positive in 69 (76.7%) patients, true negative in 10 (11.1%), false positive in 5 (5.5%), false negative in 6 (6.7%). Mean 18F-FDG PET/CT SUVmax was 6.8 ±6.2. Diagnostic sensitivity of TCT was 83.6%, specificity 82.6%, accuracy 83.3% vs. 18F-FDG PET/CT sensitivity was 92.0%, specificity 66.7%, accuracy 87.8%. A significant correlation between Ki67 and SUVmax was found in positive 18F-FDG PET/CT findings, unlike the correlation between Ki67 and Krenning score. Median PFS was 25 months (95% CI: 18.2–31.8), in 18F-FDG PET/CT positive patients 23 months (95% CI: 16.3–29.7) and 18F-FDG PET/CT negative 26 months (p = 0.279). Progression-free survival predictors were SUVmax and Krenning score.

Conclusions:
In our study, TCT and 18F-FDG PET/CT have high diagnostic accuracy in detection of NET. Higher Krenning score on TCT and SUVmax in positive 18F-FDG PET/CT findings are predictors of disease progression. 99mTc-Tektrotyd scintigraphy and 18F-FDG PET/CT can be useful complementary tools in management of patients with NETs and in predicting patients’ outcome.