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Introduction Lung neuroendocrine neoplasms (NENs) are a rare group of lung cancers that often express somatostatin receptors (SSTR2&5), with potential of diagnostic and therapeutic radiolabelled somatostatin analogues (SSAs). 99mTc-EDDA/HYNIC-TOC (Tektrotyd) is a readily available SPECT-based radiolabelled SSA that offers a cost-effective alternative with improved count rate and image resolution compared to earlier SSTR imaging agents. In lung NENs, we aim to evaluate the novel use of Tektrotyd alongside conventional assessment.Methods Single-centre retrospective analysis was conducted on 38 patients with 41 lung lesions (n=41) who underwent Tektrotyd SPECT between March 2012 and April 2023 for suspected lung NENs. Diagnostic performance metrics (sensitivity, specificity, PPV, NPV) and area under the ROC curve (AUC) were calculated and compared across Tektrotyd SPECT (n=41), 18F-FDG PET/CT (n=27), and serum Chromogranin A (CgA) (n=23). ROC analysis using Krenning scores (KS), SUVmax, and CgA levels as continuous predictors. Final diagnoses and outcomes were reviewed.Results Among 41 diagnoses, 23 were lung NENs, all confirmed with histology. 22 of them were Tektrotyd-positive (KS ≥1): typical carcinoid (n=16), atypical carcinoid (n=1), metastatic carcinoid (n=4; 2 typical carcinoid, 1 large cell neuroendocrine carcinoma, 1 pancreatic carcinoid), and DIPNECH (n=1). 1 Tektrotyd-negative (KS=0): typical carcinoid (n=1). In the 18 cases without lung NENs, there were 6 false positive and 12 true negative Tektrotyd SPECT results. Diagnostic performance metrics and ROC analyses for Tektrotyd SPECT, 18F-FDG PET/CT, and serum CgA are summarised in the figure 1. Most confirmed lung NENs (n=17) underwent surgical resection; others received SSA therapy, Everolimus, surveillance, or supportive chemotherapy.Abstract P172 Figure 1Diagnostic performance and ROC analysis for Tektrotyd SPECT, 18F-FDG PET/CT, and serum CgAConclusions Tektrotyd SPECT demonstrated superior diagnostic accuracy for lung NENs compared to 18F-FDG PET/CT and CgA testing, with particularly high sensitivity and AUC. FDG uptake often occurs in the more undifferentiated lung NENs. Hence this supports the utility of Tektrotyd SPECT as a reliable and cost-effective imaging modality for the initial evaluation and staging of suspected lung NENs. If available Ga 69 DOTATE PET/CT would of use in a similar approach. The moderate specificity and PPV suggests that positive Tektrotyd results should be reviewed in the clinical context supported by additional biomarkers and ideally confirmed by histopathology.