Proliferative activity of oxyphilic (Hurthle) cells in reactive and neoplastic thyroid lersions

The proliferative potential of oxyphilic (Hurthle) cells (HCs) present in neoplastic and non-neoplastic thyroid lesions is uncertain. To estimate the HCs ability to proliferate and to determine whether their proliferative activity correlates with the biologic behavior of different thyroid oxyphilic lesions, we selected 31 cases of chronic lymphocytic (Hashimoto's) thyroiditis and 28 oxyphilic (Hurthle cell) thyroid tumors, including 12 adenomas and 16 carcinomas. Seven histologically normal thyroid specimens from euthyroid patients served as control tissue. The proliferative activity of HCs was evaluated by means of a double immunostaining for Ki67 and a mitochondrial antigen (which specifically recognizes oxyphilic cells). Oxyphilic cells in thyroiditis had a low proliferative activity (PA: 0.55%), although higher than that of normal thyroid parenchyma (PA: 0.06%). Neoplastic HC lesions had a mean proliferative activity of 1.56% and 6.26% in adenomas and carcinomas, respectively. A statistically significant difference was observed between proliferative activity of non-neoplastic and neoplastic lesions (p<0.01), but not within the tumor group, between adenomas and carcinomas. In addition, HC carcinomas had a statistically significant positive correlation between proliferative activity and tumor size (p<0.01) and the presence of necrosis (p<0.001).