68Ga-DOTATATE PET/CT to predict response to peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumours (NETs).

Abstract

4093 Background: PRRT represents a step change in NET management, significantly improving survival. However, objective response to PRRT, approximately 20%, is poor. There are no predictive biomarkers of response. Uptake on 68Ga-DOTATATE PET/CT imaging is used to assess patient suitability for PRRT, highlighting the presence of somatostatin receptors (SSTR) to which PRRT selectively binds. We hypothesise that the density of SSTRs, as defined by a minimum SUV uptake, predicts for response to PRRT. Methods: 54 patients underwent PRRT. Modified PERCIST assessment was performed: up to 2 target lesions per organ were identified and volume of interest drawn. Maximum 5 targets were counted. Average SUV (SUVave) was calculated by dividing sum of SUVmax of target lesions by number of lesions. Response was determined by RECIST 1.1. Ki67 and SSTR2 expression were assessed on tumour samples and compared with SUVave. Results: Response to PRRT: partial response (PR) 26%, stable disease (SD) 40% progressive disease (PD) 12%. Response to PRRT predicted progression free survival (PFS) with patients experiencing PR having a PFS 2.5x that of those with SD, and almost 20x as long as PD. Using ROC curve analysis, SUVave of 21.6 predicted for tumour response with high sensitivity (0.74) and specificity (1.0), p = 0.15, 95% CI 0.71-3.96. No association between baseline SUVave and SSTR2 or Ki-67 was observed. SUVave > 21.6 was an independent predictor of clinical outcome. Conclusions: Objective response to PRRT defines a subset of patients with markedly improved PFS. SUVave 21.6 defines a threshold below which patients have a poor response to PRRT. This threshold should be taken forward into prospective study.

68Ga-DOTATATE Positron Emission Tomography-Computed Tomography Quantification Predicts Response to Somatostatin Analog Therapy in Gastroenteropancreatic Neuroendocrine Tumors

“…However, only SUVmax <18.35 remained statistically significant on multivariate analysis with hazard ratio (HR) of 6.85 (95% CI, 2.10–22.34; p = .001). When the multivariate analysis was repeated with a different 68 Ga‐DOTATATE SUVmax cutoff of 21.6, which was previously demonstrated to predict response to PRRT [19], similar results were obtained with an HR of 5.31 (95% CI, 1.63–17.33, p = .006).…”

“…Campana et al and Sharma et al each found the best 68 Ga-DOTANOC SUVmax cutoff of 17.9-19.3 and 14.5, respectively, to be an overall prognostic marker in the general GEP-NET population [16,17]. Previously proposed cutoff for predicting response to PRRT was 16.4 for 68 Ga-DOTANOC and 21.6 for 68 Ga-DOTATATE [19,20]. Although Koch et al reported a relatively higher SUVmax cutoff of 29.35 for predicting response to octreotide therapy [36], the difference is mainly attributed to the ROC curve analysis method.…”

“…SUVs on 68 Ga-DOTANOC PET/CT have overall prognostic value in the general GEP-NET population [16][17][18]. More recently, higher SUVs on 68 Ga-DOTATOC and 68 Ga-DOTATATE PET/CT were found to predict response to PRRT [19,20]. However, the role of quantitative radiotracer uptake measurements in predicting response to SSA therapy remains unclear.…”