Bilateral oncocytic malignant melanoma in axillary lymph nodes without evidence of an extranodal primary

A malignant melanoma was diagnosed in an axillary lymph node of a 49-year-old man. The tumor was examined by electron microscopy and was found to be composed of large oncocytic cells, filled with abundant mitochondria. No primary tumor could be identified on the skin or within internal organs. Approximately 2 years after the initial diagnosis, the patient presented with malignant melanoma in an axillary lymph node on the contralateral side. The second tumor also expressed the same oncocytic phenotype, favoring the common origin of both tumors. These data illustrate that oncocytic melanomas may retain their oncocytic phenotype during metastatic dissemination.