Metastatic prostatic carcinoma presenting as an oncocytic tumor.

We discuss a 63-year-old man who presented with a metastatic tumor in an inguinal lymph node. By light microscopy, the tumor cells were characterized by a finely granular eosinophilic cytoplasm. A diagnosis of metastatic oncocytic carcinoma was made based on the results of an ultrastructural examination, which showed the cytoplasm of the tumor cells to be filled with mitochondria. Results of immunocytochemical studies showed positive reactivity for prostatic acid phosphatase and prostate-specific antigen. A transurethral resection of the prostate showed an oncocytic adenocarcinoma of the prostate, apparently the first of its kind, which was demonstrated to be the site of origin of the inguinal lymph node metastasis.