Peptide receptor radionuclide therapy (PRRT) transcriptomic signature in blood for prediction of 177lu-octreotate efficacy.

4101Background: PRRT uses somatostatin receptor (SSR) expression on neuroendocrine tumors (NET) to deliver radiotherapy. Pretreatment patient stratification for response remains a key unmet need. NET transcript expression in blood integrated with tumor grade provides a PRRT predictive quotient (PPQ). This study validates the clinical utility for PRRT. Methods: Development and validation was undertaken in 3 independent 177Lu-PRRT-cohorts. Specificity and prognostic value was tested in two somatostatin analog-treated and untreated patients. Developmental cohort: lung and gastroenteropancreatic [GEP] NETs (n= 72). The majority were GEP (71%), low grade (86% G1-G2). Prospective validation cohorts (n= 42-44) were well differentiated, low grade (86-95%) lung and GEP-NETs. SSA Cohort I n= 28 (100% low grade, 100% GEP-NET); SSA Cohort II n= 51 (98% low grade; 76% GEP-NET) and an untreated cohort n= 44 (64% low grade; 91% GEP-NET). NET blood gene transcripts (n= 8: growth factor signaling and metabolism) were meas...