Mitochondria and Oncocytomas

Abstract

The designation oncocytoma was coined by Hamperl (1962) to describe a tumor composed by ‘‘oncocytes.’’ Oncocyte is a descriptive term for a neoplastic or nonneoplastic cell stuffedwithmitochondria that give a grainy, eosinophilic appearance to its swollen cytoplasm. In many instances, oxyphilic transformation is used as a synonym for oncocytic transformation, thus leading to the utilization of oxyphilic tumor as a synonym for oncocytic tumor or oncocytoma. In the thyroid, other terms are used: Hurthle cell transformation and Hurthle cell tumors (Nesland et al. 1985; SobrinhoSimoes et al. 1985, 2005). Finally, there are, in some organs, tumors composed by oncocytes that carry specific designations (e.g.Warthin’s tumor of the salivary glands). In this chapter we will only focus on neoplastic oncocytes, i.e., on the tumors – oncocytomas – composed by such cells, but they may also occur in several ‘‘normal’’ organs of elderly patients (e.g. parathyroid glands), as well as in inflammatory autoimmune disorders (e.g. Hashimoto’s thyroiditis) and in hyperplastic conditions (e.g. adenomatous goiter displaying oncocytic transformation). To be an oncocytic tumor is not a black and white phenomenon. It takes many years before the accumulation of mitochondria reaches the ‘‘oncocytic’’ threshold. In the thyroid, like in the kidney, mitochondrion-rich tumors have been described (Sobrinho-Simoes et al. 1985). The designation oncocytoma is usually used for characterizing a benign tumor, although some oncocytomas may occasionally follow a malignant course, for instance giving rise to metastases. The malignant counterpart of an oncocytoma is sometimes designated as a malignant oncocytoma. Whenever one is dealing with epithelial neoplasms, such malignant tumors may also be designated oncocytic, or oxyphilic, or Hurthle cell carcinomas. The great majority of oncocytomas – from now on we will use oncocytoma as the umbrella descriptive term for all tumors composed of mitochondrion-rich cells and oncocytic cell to designate the mitochondrion-rich cell – are epithelial-derived tumors, but