Can Complementary 68Ga-DOTATATE and 18F-FDG PET/CT Establish the Missing Link Between Histopathology and Therapeutic Approach in Gastroenteropancreatic Neuroendocrine Tumors?

Gastroenteropancreatic neuroendocrine tumors (GEPNETs) are indolent neoplasms presenting unpredictable and unusual biologic behavior that causes many clinical challenges. Tumor size, existence of metastasis, and histopathologic classification remain incapable in terms of treatment decision and prognosis estimation. This study aimed to compare Ga-68-DOTATATE and F-18-FDG PET/CT in GEPNETs and to investigate the relation between the complementary PET/CT results and histopathologic findings in the management of therapy, particularly in intermediate-grade patients. Methods: The relation between complementary Ga-68-DOTATATE and F-18-FDG PET/CT results of 27 GEPNET patients (mean age, 56 y; age range, 33-79 y) and histopathologic findings was evaluated according to grade and localization using standardized maximum uptake values and Ki67 indices. Grade 2 (G2) patients were further evaluated in 2 groups as G2a (3%- 9%) and G2b (10%-20%) according to Ki67 indices. Results: The sensitivity of Ga-68-DOTATATE and F-18-FDG PET/CT was 95% and 37%, respectively, and the positive predictive values were 93.8% and 36.2%, respectively. The sensitivity in detecting liver metastasis, lymph nodes, bone metastasis, and primary lesion was 95%, 95%, 90%, and 93% for Ga-68-DOTATATE and 40%, 28%, 28%, and 75% for F-18-FDG, respectively. Statistically significant differences were found between grades 1-2, 2a-2b, and 1-2b with respect to Ga-68-DOTATATE PET/CT as well as between 1-2a and 1-2b with respect to F-18-FDG PET/CT. However, no statistical differences were found between 1 and 2a (P > 0.05) for Ga-68-DOTATATE and 2a and 2b (P = 0.484) for F-18-FDG. The impact of the combined F-18-FDG and Ga-68-DOTATATE PET/CT on the therapeutic decision was 59%. Conclusion: Combined Ga-68-DOTATATE and F-18-FDG PET/CT is helpful in the individual therapeutic approach of GEPNETs and can overcome the shortcomings of histopathologic grading especially in intermediate-grade GEPNETs.