Asphericity of somatostatin receptor expression in SPECT/CT as a predictor of response to PRRT in neuroendocrine neoplasms

Ziel/Aim:

To assess the value of the lesion's spatial heterogeneity, quantified as asphericity (ASP), of somatostatin receptor (SSR)–expression to predict response to peptide receptor radionuclide therapy (PRRT) in patients with metastatic, SSR positive gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN).

Methodik/Methods:

From 06/2011 to 05/2013 all GEP-NEN-patients who obtained pretherapeutic In-111-DTPA-Octreotid (Octreoscan®) prior to Lu-177-DOTATATE-PRRT were retrospectively enrolled in this study. SPECT/CT of thorax and abdomen was performed on Discovery NM/CT670, GE. SSR expression in 20 NEN patients (m, n=14; f, n=6; age 54-87, mean 72.6 years) was qualitatively and quantitatively assessed by measuring Krenning Score, a metastases to liver uptake ratio (M/L ratio) and ASP. Response to PRRT was evaluated on lesion basis using RECIST 1.1 and lesion were classified as responding (RL (SD, PR, CR); n=57) and non-responding (NRL (PD); n=20). The value of Krenning Score, M/L ratio and ASP for response prediction was compared by using mann-whitney-u-test and receiver-operating-curves (ROC).

Ergebnisse/Results:

77 NEN metastases (liver n=40; lymph-node n=24; bone n=11; pancreas n=2) showed SSR expression. Higher ASP was significantly associated with poorer response (PD: 10.35±1.09; SD: 2.88±0.36; PR: 1.73±0.49, CR: 0.66±0.18; p<0.001). ROC-analyses revealed the highest ROC for discrimination between RL and NRL for ASP (AUC 0.96, p<0.001) followed by Krenning Score (AUC 0.85, p<0.001) and M/L ratio (AUC 0.82, p<0.001).The best cut-off value for ASP was <5.12 (sensitivity and specificity, 90% and 93%).

Schlussfolgerungen/Conclusions:

ASP of somatostatin expression in pretherapeutic SPECT/CT seems to be a helpful parameter to predict response to PRRT on a lesion basis in patients with metastatic NEN.