Somatostatin Receptor Scintigraphy (SRS) with 99m-Tc HYNIC-TOC

Background: This compound is a synthetic analogue of somatostatin by conjugating the Hydrazinocotinamide (Hynic) to Tyr3-Octreotide (Toc) radiolabeling via quelation with 99mTc. Purpose: We have analyzed the feasibility in detecting neuroendocrine tumors (NET) by somatostatin receptor with 99mTc Hynic-Toc. Methods: After comparative studies between 99mTc Hynic-Toc and 111In (pentetreotide) with excellent correlation, we have performed 48 scintigrams with 99mTc Hynic-Toc. 35 patients with suspicions of NET were included (19 women, 16 men. Age range 22-75 y). We have performed planar images at 1,2,24 hs and tomographic images at 150 min after intravenous injection of 740 MBq 99mTc Hynic-Toc. We compare the results with other diagnosis modalities and /or the histopathological findings after biopsy or surgery. Results: True Positive:17; True Negative:11; False Positive: 4; False Negative:3. Specificity=73.3%; Sensitivity=85%; Accuracy=80%; Not adverse effects were observed. Conclusions: 99mTc Hynic-Toc is not limited availability of the isotope. It is a suitable radiopharmaceutical for in vivo evaluation to define tumor receptor status, staging, and for identification of patients who may benefit from therapy with somatostatin. The tumor uptake at 24 hs allows a better visualization of abdominal tumor sites. Tc Hynic-Toc is an alternative to 111In-pentetreotide for imaging somatostatin receptor positive tumors. The study was offered to patients whom the scintigraphy with 111In-pentetreotide offers a diagnosis alternative with high specificity and accessible cost