Comparison of the impact of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT on clinical management in patients with neuroendocrine tumors

Abstract

This study aimed to assess the clinical impact of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG with respect to the management plan and to evaluate the prognostic value of both tracers.

Methods: a total of 104 patients (55 male and 49 female; median age, 58 y; range, 20-90 y) with histologically proven neuroendocrine tumors (NETs) underwent both ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT. Twenty-eight patients (26.9%) had poorly differentiated tumors, and 76 (73.1%) had well differentiated tumors. PET/CT results and SUVs were compared with prognostic factors such as histologic grade (G1, G2, or G3, for low-grade [well differentiated], intermediate-grade [moderately differentiated], and high-grade [poorly differentiated], respectively), chromogranin A, and proliferation index (Ki-67).

Results: the ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT findings were discordant in 65 patients (62.5%) and concordant in 39 patients (37.5%). The results changed the therapeutic plan in 84 patients (80.8%). In 22 patients (21.1%), decision making was based on the 18F-FDG findings; in 32 (30.8%), on the findings with both radiotracers; and in 50 (48.1%), on the ⁶⁸Ga-DOTATATE findings. The most frequent management decision based on ¹⁸F-FDG was initiation of chemotherapy (10 patients, 47.6%). The most common treatment decision due to ⁶⁸Ga-DOTATATE was initiation of peptide receptor radionuclide therapy (14 patients, 27.4%). In 11 (39.2%) of 28 patients with poorly differentiated NETs, the management decision was based on only the ¹⁸F-FDG results. For ⁶⁸Ga-DOTATATE, SUVmax was higher for G1 tumors and lower for G3 tumors (P 5 0.012). However, no significant differences in ¹⁸F-FDGderived SUVs were observed between different grades (P 5 0.38). The Mann-Whitney test showed significant differences in ⁶⁸Ga-DOTATATE SUVmax between tumors with a Ki-67 of less than 5% and tumors with a Ki-67 of more than 5% (P 5 0.004), without significance differences in ¹⁸F-FDG SUVmax. Log-rank analysis showed statistically significant differences in survival for patients with bone metastasis versus soft-Tissue or no metastasis for both ¹⁸F-FDG (P 5 0.037) and ⁶⁸Ga-DOTATATE (P 5 0.047). Overall survival declined rapidly with increasing grade (P 5 0.001), at an estimated 91 mo for G1, 59 mo for G2, and 48 mo for G3.

Conclusion: ¹⁸F-FDG PET/CT had no clinical impact on G1 NETs and a moderate impact on G2 NETs. However, in poorly differentiated NETs, ¹⁸F-FDG PET/CT plays a significant clinical role in combination with ⁶⁸Ga-DOTATATE. ⁶⁸Ga DOTATATE SUVmax relates to grade and Ki-67 and can be used prognostically. Key Words: ⁶⁸Ga-DOTATATE; ¹⁸F-FDG PET/CT; neuroendocrine tumors; clinical impact; prognosis.

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