4CPS-132 Understanding the types and causes of ¹⁷⁷ Lu-oxodotreotide regimen modifications to identify a typical patient profile

<h3>Background and Importance</h3> ¹⁷⁷Lu-oxodotreotide is a radiopharmaceutical indicated to treat inoperable or metastatic gastro-enteropancreatic neuroendocrine tumours (GEP-NETs) expressing somatostatin receptors. The standard treatment regimen consists of four 7.4 GBq administrations at 8 ± 1-week intervals. In certain cases, particularly because of biological toxicities, the regimen may be adapted by dose reduction, interval extension, or treatment discontinuation. These adjustments remain poorly documented in the literature, although they may concern a substantial proportion of patients. <h3>Aim and Objectives</h3> To analyse all patients treated with ¹⁷⁷Lu-oxodotreotide at a single-centre to characterise treatment regimen modifications and develop a statistical model predicting the risk of regimen changes. <h3>Material and Methods</h3> A retrospective single-centre study was conducted from May 2016 to October 2024, including all patients who received at least one cycle of ¹⁷⁷Lu-oxodotreotide for GEP-NETs, outside clinical trials or retreatment protocols. Collected data included demographic and biological characteristics, tumour-related information, and baseline laboratory parameters before each administration. Biological toxicities were graded according to NCI CTCAE v5.0. Baseline predictors of treatment modification were assessed via multivariate logistic regression. Survival was compared using a log-rank test. <h3>Results</h3> During the study period, 77 patients were treated with ¹⁷⁷Lu-oxodotreotide (M/F ratio: 1.57; mean age: 68 years). Of these, 82% had GEP-NETs and 18% had NETs of unknown or atypical origin. Treatment regimen modifications were identified in 24 patients, accounting for 38 adjustments. Nearly 25% (N=10) was toxicity-related, mainly haematologic (anaemia: 30%, thrombocytopenia: 40%, neutropenia: 10%) or renal (10%). Among inter-cycle delays (N=15), 46.7% were organisational, and 26.6% were due to toxicity. Of 13 treatment discontinuations, 53.9% were haematologic and 7.7% renal-related; two were due to newly diagnosed cancers. Neutrophil, lymphocyte, haemoglobin, platelet, albumin, and prothrombin levels, as well as bone metastases were significantly associated with the probability of treatment regimen modification. Overall survival was significantly reduced in patients with regimen modifications (log-rank p = 0.0001). <h3>Conclusion and Relevance</h3> Nearly one-third of patients experienced treatment regimen modifications, primarily due to haematologic toxicities. In the predictive model, strongly associated baseline factors were bone metastases and low platelet, haemoglobin, and lymphocyte levels. Validation using independent datasets is required to confirm the model’s reliability and potential utility in identifying patients at risk of regimen modifications. <h3>Conflict of Interest</h3> No conflict of interest