Octreotide Case 1 Answers

2) What does it bind to?

Following injection, most of the radiolabelled octreotide localises into the tissues within one hour, binding to somatostatin receptors. These receptors are normally found on many cells of neuroendocrine origin. These cells have APUD properties (amine precursor uptake and decarboxylation) and include the anterior pituitary, pancreatic islet cells, C cells of the thyroid and adrenal medulla.

Neuroendocrine tumours (including small cell tumours of the lung) have upregulated receptors and therefore bind octreotide more strongly than surrounding tissue. Some other tumours also express somatostatin receptors such as lymphomas, some brain tumours, some breast tumours, Merckel cell tumours of the skin.

Activated lymphocytes in chronic inflammation (e.g. Graves' disease & Rheumatoid Arthritis) as well as granulomatous diseases (e.g. Wegener's, Sarcoidosis and TB) also express somatostatin receptors.

Some neuroendocrine tumours such as insulinoma and medullary thyroid carcinoma are less reliably imaged (with sensitivity of ~50%). False negative results are given by de-differentiated tumours and concurrent therapy with octreotide.

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The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.