Outcomes of second round PRRT in patients with progressive refractory stage IV neuroendocrine neoplasms (NEN).

Abstract

e16331 Background: Ever since approval of PRRT for NEN in 2018, our institution has administered PRRT to around 700 patients. Seeing the rather excellent benefit – risk profile, we also trialed single or multiple repeat doses of PRRT in Stage IV patients who initially responded well but later progressed after their first PRRT round and who were either refractory to or contraindicated for other lines of therapies. The dosage, number, and interval between repeat doses was decided individually based on radiographic response and adverse effects. The aim of the study was to evaluate the safety and tolerability as well as value of the second round PRRT in this patient group. Methods: We retrospectively reviewed all patients who received a second round PRRT at our institution for refractory disease between 2018 to 2024. Multiple patient, disease, and treatment related parameters were collected, including demographic information, sites of disease, time and lines of therapies received, time points at which PRRT was received. Only patients who had both pre- and post-therapy scans within 3 months of starting/finishing second round PRRT were included. A fellowship-trained radiologist reanalyzed radiological response using RECIST 1.1. Results: Nine of a total of thirteen patients retreated met our inclusion criteria. Mean age of the study cohort was 68 yrs, 44% (4/9) were females, all ECOG 1-2, and they received up to 3 extra reduced doses of PRRT as mentioned in table 1. The average duration between the first and the second PRRT rounds was 36 +/- 14 months. 44% (4/9) patients achieved disease stability on the follow-up scans with two of them staying alive beyond 1.5 years from re-treatment. 56% (5/9) patients progressed on the first follow-up scans. Only 2 months of median CT follow-up was achieved due to mortality within 6 months for the larger segment of patients who showed refractory progression. There were not clinically significant hematologic or other adverse events. Conclusions: Second round PRRT is a safe and tolerable therapy for patients with progressive disease refractory to chemotherapy. Four out of nine patients demonstrated disease stability with two patients achieving substantial progression-free survival. Longer follow-ups are needed to assess long-term survival benefits. PRRT dosing of each patient and outcome. Patient Number and dosage (mCi) Radiographic response Outcome #1 4 – 200 & 2- 100 each Progression Death from unknown reasons # 2 4- 200 & 3- 100 each Progression Death from unknown reasons # 3 4 – 200& 2 –100 Progression Death from unknown reasons #4 6 – 200 each Stable Death from NEN #5 4 – 200 & 1-100 Stable Death from unknown reasons #6 4 – 200 & 1-100 Stable Death from unknown reasons #7 4- 200 &2-100 Stable Death from unknown reasons #8 4- 200 &1-100 Progression Death from unknown reasons #9 4-200 &1-100 progression Death from NEN