Tc99m Depreotide Scan (NeoTect): Small cell lung cancer in the left lower lobe with possible metastatic left axillary lymph node. There is some more subtle mediastinal activity as well.
Somatostatin is a 14-amino-acid peptide hormone found on many cells of neuroendocrine origin. It acts as a neurotransmitter in the central nervous system. When it binds to cells, it inhibits the release of growth hormone, insulin, glucagon, and gastrin. Somatostatin receptors have been found on the surface of many human tumor cells including APUD cells (amine precursor uptake and decarboxylation) such as pituitary tumors, pancreatic endocrine tumors, carcinoids, paragangliomas, small cell lung cancers, medullary thyroid carcinomas and pheochromocytomas. Small cell lung cancer (SCLC) tumors have neuroendocrine features. In vitro and in vivo studies have demonstrated that 50%-75% of SCLC tumors express receptors for somatostatin. Non-APUD tumor cells have somatostatin receptors, including activated lymphocytes, astrocytomas, and some breast carcinoma. Studies have shown that somatostatin analogs may inhibit growth of many of these tumors in vivo in animal studies. Tumors such as non small cell lung cancer that do not express somatostatin receptors are nonetheless imaged. One possible explanation of this finding is that the uptake of tracer is not by the receptor-negative tumor but by the surrounding tissues such as somatostatin receptor-positive white blood cells or neuroendocrine cells nearby the primary tumors. In-111-DTPA-D-Phe1]-octreotide was found to have a high affinity for somatostatin receptors . The compound, also called OctreoScan, is easily labeled with In-111. Since this radiotracer is mainly eliminated via the kidneys, intra-abdominal evaluation of somatostatin-receptor positive tumors could be performed. Tc99m Depreotide (NeoTect) is a somatostatin peptide analog labled with Technetium. FDG PET has decreased the use of somatostatin receptor scintigraphy for lung cancer.
