Mid-PRRT Response Predicts Overall Outcome in Patients with Neuroendocrine Neoplasms

Abstract Introduction – Patients with advanced well differentiated neuroendocrine neoplasm (WD-NEN) often required both peptide receptor radionuclide therapy (PRRT) with subsequent chemotherapy. Although preserving bone marrow function is vital, there are no mid-PRRT response predictors, to limit radiation exposure in patients with low predicted success rate. Purpose – To assess the utility of mid-PRRT response as a predictor for overall outcome in patients with WD-NEN. Methods - A retrospective study of WD-NEN patients that underwent ≥4 PRRT cycles. Data gathered included demographics, tumor grade, stage, and treatment response (partial response [PR], stable disease [SD] or progressive disease [PD]) evaluated by 68Ga-DOTATATE positron emission tomography (PET)/computerized tomography (CT) pretreatment, one month after 2 nd and 4 th treatment cycle, six months after 4 th cycle and at last follow-up. Results - Thirty-one patients (51.6% women, age at diagnosis 62.8±1.8 years), with pancreatic (PNEN, n=15), small intestine (SiNEN, n=9), lung (LNEN, n=2) or other (n=5) NEN received PRRT, resulting in PR (n=14), SD (n=13) and PD (n=1). Patients with PNEN had superior response vs. SiNEN (p<0.05). Patients with PR at mid-treatment had higher PR rates after PRRT completion than those with SD (p=0.004), but not six months post-PRRT or at last follow-up (p>0.05 for both). On multivariable model, adjusted for age, grade and primary site, PR at mid-treatment evaluation was associated with 10.7 adjusted odds ratio for additional PR at PRRT completion (p=0.02). Conclusion - Mid-PRRT assessment predicts subsequent response to PRRT in WD-NEN patients, allowing personalized management and reduced bone-marrow toxicity in high-risk patients.