Immunohistochemical and Clinical Assessment of Low-Risk Thyroid Tumors

Objective: Differential diagnosis and prognosis of low-risk follicular cell-derived thyroid neoplasms have been conflicting. We aimed to evaluate immunohistochemical features and prognosis of tumors in "well-differentiated tumor of uncertain malignant potential" and "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" categories.Methods: Fifty-two low-risk thyroid tumors which were classified as well-differentiated tumor of uncertain malignant potential (n = 23) and noninvasive follicular thyroid neoplasm with papillary-like nuclear features (n = 29) with a follow-up of at least 60 months were included. Galectin-3, HBME-1, CK19, and CD56 expressions were evaluated. The control group included benign nodules (n = 53), conventional papillary thyroid carcinomas (n = 37), and encapsulated follicular variant papillary thyroid carcinomas (n = 60). Results: During a median 84 months follow-up period, none of the patients experienced a recurrence of tumor. Expression of HBME-1 in low-risk tumors was significantly frequent than benign and infrequent than malignant tumors (P = .001 and P < .001, respectively). The frequency of galectin-3 positivity was similar between low-risk and malignant tumors (P = .805) and significantly higher in low-risk tumors when compared to benign nodules (P < .001). Expression of CK19 in low-risk tumors was significantly frequent than benign nodules and infrequent than malignant tumors (P = .01 and P = .001, respectively). The expression profile of CD56 was similar in benign nodules and low-risk tumors (P = .361). Total loss of CD56 in tumor was the most specific marker of malignancy (100%). Positive staining of HMBE-1 was the most sensitive marker (89.7%) for predicting malignancy.Conclusion: Low-risk thyroid tumors had immunohistochemical features overlapping with both benign and malignant thyroid tumors and had a benign course of disease during a long follow-up period.