Comparison of octreotide scintigraphy and conventional imaging in medullary thyroid carcinoma

We evaluated the clinical utility of positive somatostatin receptor scintigraphy in patients with medullary thyroid cancer (MTC).

Twenty-four MTC patients with increased calcitonin levels underwent somatostatin receptor scintigraphy using 111In-pentetreotide (120-200 MBq) with early (4 hr after injection) and delayed (24 hr) whole-body scans and liver SPECT imaging. In Group 1 (12 patients), conventional imaging modalities demonstrated the presence of tumor sites prior to somatostatin receptor scintigraphy; in Group 2 (12 patients), conventional imaging modalities were negative or inconclusive.

Somatostatin receptor scintigraphy had positive results in 9 of 24 patients (37%): of Group 1 patients, 7 of 12 had positive somatostatin receptor scintigraphy results. Of these patients cases, somatostatin receptor scintigraphy demonstrated several involved organs and tumor sites either identical (two patients) or smaller (five patients) in size than conventional imaging modalities. Only two patients in Group 2 had positive somatostatin receptor scintigraphy results which demonstrated significant mediastinal uptake previously classified as indeterminate on conventional imaging modalities. No new tumor site was identified nor were therapeutic options modified by the somatostatin receptor scintigraphy results.

Somatostatin receptor scintigraphy only demonstrates part of tumor sites and cannot visualize small tumor sites (< or = 1 cm). We believe that somatostatin receptor scintigraphy has a limited role in the management of MTC patients.