Gray zone thyroid tumors for which benignity or malignancy cannot be assessed are constantly increasing and accurate prediction of their malignant behavior is vital to avoid both violent surgical intervention for benign tumors and lax treatment of malignant tumors. The retrospective study included 120 blocks of thyroid lesions; 60 patients underwent partial thyroidectomy for query atypical adenoma and 60 blocks of complementary thyroidectomy of the same patients. Complementary thyroidectomy blocks included 21cases of thyroid cancer and 39 cases were multinodular goiter, while partial thyroidectomy blocks included 15 cases of thyroid adenoma, 17 cases were colloid nodules and 28 cases were tumors of uncertain malignant potential (TUMP). The expression levels of both telomerase reverse transcriptase (TERT) promoter mutations and proEx C antibodies were assessed in all blocks; analysis and correlation of marker expression of both groups (complementary and partial thyroidectomy) were done. 20 patients out of 28 suffering from TUMP developed thyroid carcinoma. Ten of them had positive TERT promoter mutation, all of which turned into cancer thyroid in a mean time of 8.2 ±2.61 years, and seventeen who a had high proEx C labeling index (LI) underwent a malignant transformation in 7.52 ±1.17 years in a shorter time than the group with negative TERT/proEx C expression which transformed within 12.31 ±3.57 years, whereas only one case diagnosed first as thyroid adenoma transform into thyroid carcinoma. TERT promoter mutation and proEx C expression are promising markers for determining the malignant potential in tumors of uncertain malignant potential.