oncocyte

An oncocyte is an epithelial cell characterized by an unusually abundant, finely granular eosinophilic cytoplasm, which is due to a high content of mitochondria. The cytoplasm appears intensely pink and granular on routine stains, while the nuclei are typically small and centrally located. Oncocytes can be found singly or in clusters and may be present in both non-neoplastic and neoplastic tissues. When a tissue shows widespread oncocytic change, it is said to have oncocytic metaplasia or oncocytosis.

Histologically, oncocytes have an enlarged, granular cytoplasm that reflects mitochondrial proliferation. In special studies, electron microscopy confirms numerous and enlarged mitochondria. Immunohistochemical and ultrastructural patterns vary with tissue type, but the defining feature remains the mitochondrial-rich cytoplasm. The presence of oncocytes can be a key diagnostic clue, particularly when they form the characteristic architecture of a specific tumor or lesion.

Oncocytes occur in several organs and are associated with a number of conditions and tumors. In the salivary glands, oncocytic epithelium is seen in Warthin tumors and other oncocytic lesions. In the thyroid, Hurthle (oncocytic) cells are seen in Hashimoto thyroiditis and in Hurthle cell neoplasms. In the kidney, renal oncocytoma is a benign tumor composed of oncocytes, while oncocytic variants can occur in some renal carcinomas. Oncocytic change can also appear in liver and other tissues, either as metaplastic/benign processes or within neoplasms. The recognition of oncocytes aids differential diagnosis and may influence management, as oncocytic neoplasms range from benign to malignant depending on the organ and entity.