Comparison of 18F-FDG PET and 99mTc-TOC scintigraphy in patients with neuroendocrine tumor

Objectives This study was designed to investigate the complementary value of 18F-FDG PET/CT to 99mTc-EDDA/HYNIC-TOC (99mTc-TOC) scintigraphy in detection of neuroendocrine tumor.

Methods Twenty-eight patients (14 M, 14 F; 19-70 y) with histological confirmed neuroendocrine tumors were included. All patients underwent both 99mTc-TOC scintigraphy and 18F-FDG PET/CT scan within 2 weeks. The patients were divided into single-tumor group (n = 13) and multiple-tumor group (n = 15) for comparison. Standardized uptake values (SUVs) of 18F-FDG positive lesions and tumor to liver ratios of 99mTc-TOC positive lesions were measured for semi-quantitative analysis.

Results In case-based analysis, the sensitivity of 99mTc-TOC scintigraphy was 85.7% ( 24/28), while 18F-FDG PET/CT had positive findings in 96.4% (27/28) patients. The patient misdiagnosed by PET had a single tumor <1 cm in the lung. In lesion-based analysis, 18F-FDG PET detected 87/88 (98.9%) of tumor foci, and the maximum SUVs in lesions with multiple tumors were significantly higher than those in patients with single tumor (8.04±4.98 vs. 3.35±1.61, P=0.002). On the other hand, 99mTc-TOC scintigraphy only identified 55/88 (62.5%) of the tumors, and it showed higher sensitivity in detection of tumors in single-tumor group than in multiple-tumor group (84.6% vs. 57.9%). In spite of the small tumors that was more easily to be negative, 99mTc-TOC scintigraphy usually missed the lesions at lymph nodes (77.8%) and bones (81.0%). In the 15 patients with multiple tumors, the staging and clinical management of 5 patients were changed by 18F-FDG PET/CT.

Conclusions 18F-FDG PET/CT is a sensitive method to complement 99mTc-TOC scintigraphy for detection of neuroendocrine tumors. For the patients with multiple tumors, it may change the management by finding more lesions, especially for lymph node and bone involvement