Somatostatin scintigraphy is an imaging technique that has become the gold standard for imaging carcinoid and related neuroendocrine tumors. It's an isotope scan, in essence, which entails the use of indium-111 attached to a ligand, which is an analog of somatostatin.

The tumor cells have receptors for somatostatin on their surface. There are five categories of receptors, 1 through 5. The commercially available preparation called OctreoScan is attracted specifically to type 2 receptor and, to a somewhat less extent, to type 5 receptor. This scan images approximately 85% of carcinoids and nearly as many of the other neuroendocrine tumors, with a few exceptions.

This scan has been available, for roughly a decade. It's used widely, both to diagnose and to stage these tumors, and also to confirm the completeness of resection or the regression of tumors after various types of ablative treatment or chemotherapy.

There are some false positives that can occur, particularly in active granulation tissue immediately postoperatively or with certain diseases such as sarcoid or even Crohn's disease. Some infections will also light up on this scan. There are other applications, as well. For example, in a difficult, obscure tumor which lights up on the standard scintigraphy examination, but is not imaged by MRI or CT scan, we may be able to find it by doing a very special handheld gamma detector scan intraoperatively.

There are uses besides diagnosis, too. For example, if a patient is to be considered for liver transplant, we should like to know that their tumor is free of any extrahepatic metastases. And so the OctreoScan will help to discern if lesions are limited to the liver.

In addition to that, we can also determine in advance whether or not there's going to be a beneficial response to octreotide treatment or to other somatostatin analog treatment. Those tumors which have an abundance of type 2 receptors and light up well are most likely to respond well to treatment with these drugs.

Richard Warner MD