Oncocytic Cells: Nature and Significance

Oncocytic cells are thyroid follicular cells characterized by abundant finely granular eosinophilic cytoplasm and enlarged nuclei. “Oxyphilic” and, in the thyroid gland, “Hürthle” cells are synonymous, but the oncocytic terminology is preferable and consistent with the most recent WHO classification of thyroid neoplasms (1). The cytoplasmic characteristics reflect the massive accumulation of mitochondria (Figure 1) caused by mitochondrial and nuclear DNA alterations perturbating pathways involved in the oxidative phosphorylation (2, 3). The metabolic properties of oncocytic cells are responsible for the loss of specificity of PET/CT fluorodeoxyglucose (FDG) scan that has been proposed to predict malignancy in thyroid nodules. In fact, the glucose uptake is increased in mitochondria-rich cells, irrespective of their neoplastic biological behavior. In some studies, the exclusion of oncocytic cell lesions increased the risk of malignancy in FDG PET/CT positive lesions from 38% to 68% (4)