Clinicopathologic characteristics of synchronous primary thyroid cancer detected by initial staging 18F-FDG PET-CT examination in patients with underlying malignancy.

BACKGROUND: The objective of this study was to define clinicopathologic characteristics in concurrent primary thyroid cancer detected by initial (18)fluorine-fluorodeoxyglucose positron emission tomography-computed tomography ((18)F-FDG PET-CT) scanning in patients with underlying malignancy. PATIENTS AND METHODS: Among 155 patients with known underlying malignancy and with focal FDG uptake in the thyroid, 25 patients (22 females; mean age ± SD 54.4 ± 11.2 years; age range 27-70 years) who were confirmed as having papillary thyroid cancer (PTC; synchronous thyroid cancer) by cytological examination were included. Another 25 patients (24 females; mean age ± SD, 48.8 ± 12.7 years) with focal uptake in preoperative (18)F-FDG PET-CT due to PTC and no history of other malignancy (primary thyroid cancer) were also included. Immunohistochemical studies were performed for glucose transporter-1 (GLUT-1) and vascular endothelial growth factor (VEGF).
RESULTS: GLUT-1 expression was significantly lower in synchronous thyroid cancer (7 of 25 patients, 28%) compared with primary thyroid carcinoma (15 of 25 patients, 60%; p = 0.045). However, age and tumor size of synchronous thyroid cancer were not significantly different from the patients with primary thyroid carcinomas. There was no significant difference in VEGF expression, maximal standardized uptake values, extrathyroidal extension, lymph node metastasis, advanced stage, and multifocality between both thyroid cancer groups.
CONCLUSION: Clinicopathologic characteristics of synchronous thyroid cancer in patients with underlying malignancy were not different from those of patients with primary thyroid cancers except for GLUT-1 expression.