e16317 Background: NETs are rare tumors commonly originate from the gastrointestinal (GI) tract, pancreas, lung, and other sites. 177 Lu-PRRT was approved in 2018 for treatment of pts with GI or pancreatic NETs. Here we report our institutional experience in advanced NETs pts treated with PRRT and explore whether NETs of different primary sites and certain metastatic sites (liver, peritoneum, bone) respond to PRRT differently. Methods: This was a retrospective observational study evaluating the response of different primary and metastatic sites to 177 Lu–PRRT in 209 adult pts with NETs treated between Jan 1, 2015 and Mar 31, 2025. Data were collected from the electronic health record. Eligible pts were ≥18 years old, histologically confirmed metastatic NET, received at least one cycle of 177 Lu-PRRT, and had baseline and post-treatment imaging available for response assessment. Primary endpoint was overall response rate (ORR) following completion of PRRT. Secondary endpoints included overall survival (OS), progress-free survival (PFS), disease control rate (DCR), and site-specific response. Response was evaluated on imaging obtained after the final administered dose. Descriptive statistics summarized patient and disease characteristics, and multivariable regression models were used to account for potential confounding, including age, tumor grade, primary tumor site, metastatic burden, and prior systemic therapies. Results: Median age was 66 (57-72). Over half (53%) were male. The majority (71%) were Caucasian, 26% were Black. Half of the pts (49.3%) had grade (gr) 2 disease, 24.4% had gr 1, 12.2% of pts had gr 3. For the entire cohort, the median OS was 56.0 months (mo, range 50.0-64.0), median PFS was 10.0 mo (9.0-13.0). Complete response (CR) was seen in 1.5% of pts, 34.9% of pts had partial response (PR), 52.0% of pts had stable disease (SD), with progressive disease (PD) in 11.6% of pts. The overall DCR was 88.4%. The ORR according to primary site was 24.7% in GI (n = 97), 52.5% in pancreas (n = 40), 23.1% in lung (n = 13), 0% in other (n = 2), and 52% in unknown primary (n = 25). DCR according to primary site was 85.6% in GI, 85.0% in pancreas, 92.3% in lung, 100.0% in other, and 92.0% in unknown primary. The best response of liver, peritoneal, and bone metastases (mets) are summarized in Table 1. Conclusions: In this single-institution study, pts with pancreatic and unknown primary had a higher ORR to 177 Lu-PRRT compared to pts with other primaries. Response to PRRT is commonly seen in liver mets. Peritoneal and bone mets have a lower response rate but stable disease is achieved in the majority of pts. Best response of liver, peritoneal, and bone mets. Metastatic Site N CR (%) PR (%) SD (%) PD (%) Liver 187 2 (1.1) 58 (32.8) 94 (53.1) 23 (13.0) Peritoneum 78 0 (0) 19 (25.3) 49 (65.3) 7 (9.3) Bone 117 1 (0.9) 16 (15.0) 79 (73.9) 11 (10.3)
Shah et al. (Thu,) studied this question.