Purpose: This study aimed to test the role of combined imaging with 18F-FDG-PET/CT and 111In-octreotide SPECT in characterizing thymic epithelial tumors (TETs).
Methods: We evaluated 20 patients with newly diagnosed TETs who had undergone concomitant 18F-FDG-PET/CT and 111In-octreotide SPECT. Thymic epithelial tumors were classified by World Health Organization (WHO) as low-risk thymomas (5), high-risk thymomas (4), and thymic carcinomas (11, among which 6 neuroendocrine tumors). Patients were staged according to Masaoka system. 18F-FDG-PET/CT was performed and SUVmax of primary tumors was recorded. 111In-octreotide SPECT of the thorax was performed, and tumor-to-background ratio was determined on the 24-hour coronal sections.
Results: All patients showed increased 18F-FDG uptake in mediastinal lesions. SUVmax were significantly correlated with WHO classification (r = 0.66, P < 0.01) and with Masaoka stage (r = 0.60, P < 0.01). SUVmax of low-risk thymomas (mean [SD], 2.87 [0.83]) were significantly lower than those of high-risk thymomas (mean [SD], 7.21 [1.73], P < 0.01) and of thymic carcinomas (mean [SD], 9.39 [5.80], P < 0.05), whereas no significant difference was found between high-risk thymomas and thymic carcinomas. SUVmax of all high-risk thymomas and thymic carcinomas was 4.5 or greater. All primary tumors were detected by 111In-octreotide SPECT, and tumor-to-background ratios ranged between 1.67 and 10.10. No statistically significant correlation was found between tumor-to-background ratios and WHO classification (r = 0.24, P = 0.36) and Masaoka stages (r = 0.31, P = 0.23). However tumor-to-background ratios of thymic neuroendocrine tumors (mean [SD], 5.71 [3.09]) were significantly higher than those of all other TETs with SUVmax of 4.5 or greater (mean [SD], 2.41 [0.56]; P < 0.05).
Conclusions: 18F-FDG-PET/CT scan allows to differentiate high-risk epithelial tumors and thymic carcinomas from low-risk thymomas, whereas 111In-octreotide SPECT may identify neuroendocrine tumors among those showing high 18F-FDG uptake.
From the *Department of Biomorphological and Functional Sciences, University of Naples Federico II; †Institute of Biostructures and Bioimages, National Research Council; ‡Department of Endocrinology and Molecular and Clinical Oncology, University of Naples Federico II; §Rare Tumors Excellence Center, University Hospital Federico II, Naples; and ¶Department of Medicine and Surgery, University of Salerno, Salerno, Italy.
Received for publication September 10, 2012; revision accepted December 29, 2012.
Partly supported by the Ministry of Instruction, University and Research (MIUR), Medical Research in Italy (MERIT), project no. RBNE08YFN3 by Associazione Italiana per la Ricerca sul Cancro (AIRC, project no. 11756), and by the Regione Campania fund for “Rare Tumors Excellence Center.”
Conflicts of interest and sources of funding: none declared.
Reprints: Silvana Del Vecchio MD, Department of Biomorphological and Functional Sciences, University of Naples Federico II, Via Pansini 5 Edificio 10, 80131 Napoli, Italy. E-mail: firstname.lastname@example.org.