IN-VIVO DETECTION OF MALIGNANT THYMIC MASSES BY INDIUM-111-DTPA-D-PHE(1)-OCTREOTIDE SCINTIGRAPHY

Many tumors with neuroendocrine characteristics express high amounts o f somatostatin receptors that enable in vivo imaging with [(111) In-DT PA-D-Phe(1)]-octreotide. In this study, we have analyzed the feasibili ty in detecting and characterizing thymic masses by somatostatin recep tor scintigraphy (SRS), Methods: Eighteen patients (13 women, 5 men, a ges 18-78 yr; mean +/- s.d. = 42.1 +/- 17.6 yr) were enrolled in this study, Eleven patients were studied during diagnosis and seven during routine follow-up, In seven patients, myasthenia gravis was the presen ting symptom. SRS was performed within 4 wk after CT and/or MRI, Plana r and tomographic images were acquired within 24 hr after the injectio n of approximately 111 MBq of [(111) In-DTPA-D-Phe(1)]-octreotide. The scintigraphic results were categorized according to the histologic fi ndings, Results: Histology diagnosed 10 mixed epithelial/lymphoid thym omas (8 with prevalent epithelial component), 2 thymic carcinomas, 1 t hymic carcinoid, 1 lymphangioma and 4 thymic hyperplasias. Two thymoma were Stage I, 3 were Stage II, 2 were Stage III and 5 were Stage IV, as was the thymic carcinoid. Indium-111-DTPA-D-Phe(1)-octreotide conce ntrated in primary and/or metastatic sites of thymic tumors, thereby e nabling successful external gamma imaging of sites greater than 1.5 cm in size, Tumor-to-lung (T/L) ratios were as high as 7.6-fold (range 1 .7-7.6). Untreated thymomas showed higher T/L (4.34 +/- 1.57) than tre ated ones (2.68 +/- 1.18). No uptake was detectable in the four patien ts with benign thymic hyperplasia and the patient with the lymphangiom a. Conclusion: Indium-111-DTPA-D-Phe(1)-octreotide is avidly concentra ted within thymic tumors, but it is not concentrated by thymic hyperpl asia, which allows differential diagnosis. Thus, in patients with myas thenia gravis, SRS may have a role in characterizing thymic masses, th ereby overcoming the limits of cross-sectional imaging modalities.