Thyroid tumors of uncertain malignant potential (TT-UMP) comprise an accepted subgroup of follicular-patterned thyroid tumors for which benignancy or malignancy cannot be precisely assessed. We aimed to evaluate the demographic characteristics, ultrasound (US) findings, and cytological results of patients with TT-UMP and compare these findings to a classical variant of papillary thyroid carcinoma (CV-PTC) and non-encapsulated follicular variant of PTC (NEFV-PTC) patients; we also evaluated the immunohistochemical characteristics of patients with TT-UMP. Twenty-four patients with TT-UMP, 672 with CV-PTC, and 132 with NEFV-PTC were included in the study. Mean longitudinal nodule size and median nodule volume were higher in the TT-UMP group than in the CV-PTC and NEFV-PTC groups (p < 0.001 and p < 0.001 for CV-PTC; p < 0.001 and p = 0.008 for NEFV-PTC). The presence of halo and peripheral vascularization was observed more frequently in the TT-UMP group than in the CV-PTC group (p = 0.002 and p = 0.024). Benign and follicular neoplasm/suspicious for follicular neoplasm cytological results were higher in the TT-UMP group than in the CV-PTC group (p = 0.030 and p = 0.001). US findings were similar between TT-UMP and NEFV-PTC groups (all, p > 0.05). However, none of the patients with TT-UMP were called malignant; 105 patients (31.2 %) of CV-PTC and 11 patients (9.5 %) of NEFV-PTC (infiltrative FV) were classified as malignant cytologically. Tumor size was higher in the TT-UMP group than in the CV-PTC and NEFV-PTC groups (p < 0.001 and p = 0.006). In the TT-UMP group, positive expression of HBME-1, CK-19, and Gal-3 was found in 50, 33.3, and 25 % of patients, respectively. This study demonstrated that none of the TT-UMP patients were evaluated as malignant in preoperative cytology. However, patients with TT-UMP had higher nodule and tumor sizes than CV-PTC and NEFV-PTC patients; US features were similar between NEFV-PTC and TT-UMP patients.
Keywords: Classical variant of papillary thyroid carcinoma; Cytology; Non-encapsulated follicular variant of papillary thyroid carcinoma; Thyroid tumors of uncertain malignant potential; Ultrasound.