Somatostatin receptor scintigraphy of a patient with a giant invasive prolactinoma.

A 41-year-old with a giant prolactinoma underwent in-111 pentetreotide (Octreotide) imaging showing very intense tracer uptake in the region of the anterior skull base. In contrast, there was no significant response to Octreotide therapy. Prediction of clinical responsiveness to Octreotide therapy in patients with pituitary adenomas may depend on the presence of somatostatin receptor subtype 5. Pentetreotide does not avidly bind to this receptor subtype and therefore, cannot be used clinically to predict therapeutic Octreotide responsiveness in patients with large prolactinomas.