An OctreoScan is fairly straightforward. While it cannot give an indication as to tumor size, it can indicate the extent of disease metastasis and show possible loci for tumors which may or may not have been suspected. Essentially what happens is this: about 4 to 24 hours prior to scanning, a Nuclear tag (about 6 milliCuries) piggybacked onto a somatostatin analog (like Sandostatin) is injected.
This tag is then taken up by any tissue exhibiting a type two receptor. Usually you find type two receptors in carcinoid cancers, liymphomas, some breast cancers and so on. The body of the person is then scanned at 24, 48 and possibly 72 hours or whenever the oncologist and radiologist deem it beneficial. The tag being tumor-specific will cause any tissue with the requisite receptors to light up on the scan film. The test is sort of go or no-go.
Most carcinoid tumors have the receptors and light up the film; about 2 percent of tumors do not have the receptors and thus do not show up. If the patient is on a somatastatin medication such as Sandostatin, the receptors will be blocked and the tumors will not show up. Sandostatin has to be stopped about 3 days prior to scanning for an accurate test to be performed.