Characterizing an ectopic secreting carcinoid with indium-111-DTPA-D-Phe-pentetreotide.

Unlabelled: This report describes a technique that increases the specificity of 111In-pentetreotide as evaluated in a patient with ectopic Cushing syndrome.

Methods: Two separate SPECT studies were performed with different pharmacologic protocols, both including treatment with cold octreotide. The imaging protocol provides acquisitions at 4 and 24 hr after injection. The quantitative approach was based on the ROI activity (manually designed) of an area of pathological lung uptake (ROI-T) versus background (ROI-NT). Histological, histochemical and specific mRNA measurements confirmed the presence of an SSR2 receptor carcinoid in the lung.

Results: The time course of ROI-T/ROI-NT is a linear increase between 4 and 24 hr. Washout with cold octreotide diminished the ROI-T activity content and the saturation protocol increased ROI-T/ROI-NT, confirming the specific nature of the uptake.

Conclusion: Displacement and saturation protocols in 111In-pentetreotide imaging demonstrated the specificity of tumor binding.