Correlation of clinical and pathological findings and SUVmax value of initial F-18 FDG PET/CT of primary papillary thyroid carcinoma: A potential new risk factor

Objectives Thyroid cancer represents the vast majority of endocrine cancers and its incidence is increasing. Most papillary thyroid carcinoma (PTC) has an excellent prognosis if diagnosed early and treated appropriately. A significant number of PTC, despite excellent prognosis, show aggressive features such as extrathyroidal extension and lymph node metastasis that may not always be detected preoperatively or intraoperatively. The aims of this study are to analyze clinical and pathologic variables affecting SUVmax of primary PTC on preoperative F-18 FDG PET/CT.

Methods From March 2005 to December 2010, 148 newly diagnosed patients with PTC (female=121, mean age: 49.0±13.0 years) underwent F-18 FDG PET/CT for initial evaluation were enrolled in this retrospective study and all patients were diagnosed with PTC by postoperative permanent biopsy. The clinical and pathologic characteristics that influence the F-18 FDG PET/CT findings in these patients were analyzed with respect to the following variables: age, sex, tumor size, multifocality of the primary tumor, perithyroidal invasion and lymph node metastasis of neck-based final pathology.

Results Patients with tumor size ≥ 1cm, lymph node metastasis (+), perithyroidal invasion (+) and high risk group showed significantly higher SUVmax (10.4±8.1, 9.5±8.3, 9.8±8.1 and 9.0±7.6) than those of patients with size < 1cm, lymph node metastasis (-), perithyroidal invasion (-) and low risk group (3.8±2.2, P<0.0001; 6.6±5.8, P=0.018; 5.8±5.4, P<0.0001; 5.3±5.1; P=0.001). However, there was no significant difference between SUVmax and age, multifocallity and direct invasion to adjacent organ.

Conclusions Tumor size, lymph node metastasis, perithyroidal invasion and high risk group of DTC can influence SUVmax of primary PTC lesion. The SUVmax of primary PTC lesion can be used to predict high risk group.