Aim/introductionPeptide receptor radionuclide therapy (PRRT) is an effective and well-tolerated treatment option for patients with neuroendocrine tumors (NETs) that prolongs progression-free survival (PFS). However, the limited overall survival (OS) rates in the prospective phase III study (NETTER1) highlighted the need to identify patient-specific long-term prognostic markers to avoid unnecessary side effects and enable better treatment stratification. Therefore, we retrospectively analyzed prognostic risk factors in NET patients treated with PRRT.MethodsA total of 62 NET patients (G1: 33.9%, G2 62.9%, and G3 3.2%) with at least 2 cycles of PRRT with [177Lu]Lu-HA-DOTATATE (mean 4 cycles) were analyzed. Of which, 53 patients had primary tumors in the gastroenteropancreatic (GEP) system, 6 had bronchopulmonary NET, and 3 had NET of unknown origin. [68Ga]Ga-HA-DOTATATE PET/CT scans were performed before PRRT start and after the second treatment cycle. Different clinical laboratory parameters, as well as PET parameters, such as SUVmean, SUVmax, and PET-based molecular tumor volume (MTV), were collected, and their impact on the OS was investigated. Patient data with a mean follow-up of 62 months (range 20–105) were analyzed.ResultsAccording to interim PET/CT, 16 patients (25.8%) presented with partial response (PR), 38 (61.2%) with stable disease (SD), and 7 (11.3%) with progressive disease (PD). The 5-year OS was 61.8% for all patients, while bronchopulmonary NETs showed poorer OS than GEP-NETs. Multivariable Cox regression analysis showed that chromogranin A level and MTV together were highly significant predictors of therapeutic outcome (HR 2.67; 95% CI 1.41–4.91;p= 0.002). Treatment response was also influenced by the LDH level (HR 0.98; 95% CI 0.9–1.0;p= 0.007) and patient age (HR 1.15; 95% CI 1.08–1.23;p< 0.001). ROC analysis revealed baseline MTV > 112.5 ml [Sens. 91%; Spec. 50%; AUC 0.67 (95% CI 0.51–0.84,p= 0.043)] and chromogranin A >1,250.75 μg/l [Sens. 87%; Spec. 56%; AUC 0.73 (95% CI 0.57–0.88,p= 0.009)] as the best cutoff values for identifying patients with worse 5-year survival.ConclusionOur retrospective analysis defined MTV and chromogranin A in combination as significant prognostic factors for long-term OS. Furthermore, an interim PET/CT after two cycles has the potential in identifying non-responders who may benefit from a change in therapy at an early stage.