Clinical validation and diagnostic accuracy of (99m)Tc-EDDA/HYNIC-TOC compared to (111)In-DTPA-octreotide in patients with neuroendocrine tumours: the LACOG 0214 study

(99m)Tc-EDDA/HYNIC-TOC is an easily available and cheaper radionuclide that could be used for somatostatin-receptor-based imaging of neuroendocrine tumours (NETs). We aimed to evaluate the diagnostic performance of (99m)Tc-EDDA/HYNIC-TOC compared to(111)In-DTPA-octreotide in patients (pts) with NETs. We performed a prospective diagnostic study including pts with biopsy-confirmed NET and at least one visible lesion at conventional imaging. Two independent nuclear medicine physicians evaluated pts who underwent (99m)Tc and (111)In scans and images. The primary outcome was comparative diagnostic accuracy of (99m)Tc and (111)In. Secondary outcomes include safety. Nine pts were included and performed 14 paired scans. Overall, 126 lesions were identified. (99m)Tc demonstrated superior sensitivity both when all images were analysed (93.7, 95% CI 88.1% – 96.8% versus 74.8%, 95% CI 66.6 – 81.6%, p < 0.001) and when liver-specific images were analysed (97.8%, 95% CI 92.7% – 99.5% versus 85.1%, 95% CI 76.6% – 91.0%, p < 0.001). (99m)Tc was also associated with a lower negative likelihood ratio (LR) (0.002, 95% CI 0.009 – 0.1 versus 0.19, 95% CI 0.12 – 0.42, p = 0.009) when evaluating hepatic lesions. Adverse events happened in 3 pts after (111)In and in 2 pts after (99m)Tc, all grade 1. The (99m)Tc demonstrated a higher sensitivity overall and a better negative LR in liver-specific images compared to (111)In in pts with NETs. Our findings suggest that (99m)Tc is an alternative to (111)In and is especially useful in ruling out liver metastases. NCT02691078.