THU508 Does Mid-treatment Response To 177Lu-DOTATATE Predict Treatment Outcome In Patients With Neuroendocrine Neoplasms?

Disclosure: R. Halperin: None. A. Tirosh: None. Introduction - Patients with advanced or unresectable neuroendocrine neoplasm (NENs) have limited systemic treatment modalities. Among these, patients with well differentiated (G1 and G2) NENs can be treated with peptide receptor radionuclide therapy (PRRT) treatment with 177Lu-DOTATATE. However, a subset will require further chemotherapy in later stages. Hence, limiting radiation exposure is of paramount importance. However, there are no mid-term predictive factors for response to PRRT. Aims - Assess the utility of mid-treatment (post 2(nd) cycle) response to PRRT as a potential predictor for final outcome in patients with well-differentiated NENs. Materials and Methods - A retrospective study in a tertiary center, enrolling patients that underwent at least four cycles of PRRT. Data gathered included demographics, tumor grade and stage, treatment response (partial response [PR], stable disease [SD] or progressive disease [PD]) evaluated by 68Ga-DOTATATE PET CT after 2(nd) and 4(th) treatment cycle, compared to pretreatment 68Ga-DOTATATE PET CT scan. Results - A total of 30 patients (50% women, age at diagnosis 63.5±1.7 years) completed four PRRT cycles (median, range 4-6). NEN primary site were pancreatic (n=15), small intestine (n=8), lung (n=2) or other (n=5). Final outcome was PR, SD and PD in 15, 13 and 2 patients, respectively. Patients with pancreatic NEN had superior response vs. small intestine NEN (p=0.01). Patients with PR at mid-treatment had higher PR rates at final evaluation than those with mid-term SD (p=0.008). On multivariable model, adjusted for age at diagnosis, grade, NEN type, and medical treatment, mid-treatment outcome was independently associated with final outcome (adjusted odds ratio 9.1, 95% confidence interval 1.4-60.4, p=0.02). Conclusions - Mid-treatment PRRT efficacy can serve as a measure of final outcome in patients with advanced or unresectable well differentiated NEN. Presentation: Thursday, June 15, 2023