Endocrine Abstracts

Introduction: Somatostatin analogues (SSA) are recommended as the first-line systemic therapy, to control tumour growth for advanced or metastatic well-differentiated neuroendocrine tumours (WD NET), with good expression of the somatostatin receptors. [68Ga]Ga-DOTA-SSA PT/CT has become the gold standard in the diagnosis, staging and monitoring therapy, of WD NET.

Aim: The aim of the study was to evaluate the predictive role of standardized uptake values (SUVs) and volumetric parameters obtained from pretreatment [68Ga]Ga-DOTA-SSA for response to SSA therapy, in patients with NET.

Material and Methods: 42 patients (21 women, 21 men; age range: 46-84 years) with histologicall, confirmed, metastatic, NET (15 pancreatic, 15 small-intestinal, 4 lung, 7 unknow, 1 cecum; WHO G1 13, G2 28, 1 unknown; median Ki-67 index 5%, range 1-16) who received long acting SSA as a first line treatment were included to the study. All of them underwent [68Ga]Ga-DOTA-TATE PET/CT before receiving SSA as a first-line treatment. For each [68Ga]Ga-DOTA-TATE avid lesion, SUVmax and SUVmean were measured as well as TBR was calculated as SUVmean of tumours/metastases divided b, SUVmean of normal spleen. Furthermore, two volumetric parameters were calculated: somatostatin receptor expression tumour volume (STV) and total lesion somatostatin receptor expression (TLD). Finally the sum of STV (total STV, TSTV) and TLD (total TLD, TTLD) was calculated for each patient and used in the analysis.

Results: At the time of the analysis, 14 patients showed stable disease (33,3%), 28 patients were progressive (66,7%); among whom 12 patients died. The median progression-free survival (PFS) and overall survival (OS) were 26.5 and 46.5 months, respectively. The median SUVmax, SUVmean and TBR ratio was 38.5 (range 12.9-99.1), 21.4 (range 10.4-51.9) and 0.93 (range 0.38-3.29), respectively. The median TSTV was 41.4 cm³ (range 1.0-1446.7) and the median TTLD was 650.7 (range 10.6-16156.8). In the univariate analysis, in the whole population study TBR ratio (HR=1.96, 95% CI 1.058-3.62, P=0.03) was the only, parameters that was significantly, associated with PFS. Among patients with small intestinal NETs, TSTV (HR=1.00, P=0.023) and TTLD (HR=1.00, P=0.026) were significantly, associated with PFS in the univariate analyses. No significant correlation was found between measured volumetric parameters and OS.

Conclusions: >Standardized uptake values and volumetric parameters of pretreatment 68[Ga]Ga-DOTA-TATE PET/CT may, be potentially, useful in prediction of the response to SSA (used in monotherapy, as a first-line therapy,) in patients with NET.