Metastatic Leydig cell tumor with sarcomatoid differentiation.

Leydig cell tumors of the testis are uncommon. Only about 10% of cases have a malignant course. It has been stated that the only definite criterion for malignancy is presence of metastasis. We present a 47-year-old patient with metastatic Leydig cell tumor 17 years after initial diagnosis, to our knowledge the longest reported interval between diagnosis and the development of metastasis. The primary tumor did not exhibit convincing features of malignancy. The initial metastasis in the right perirenal fat tissue showed a biphasic tumor with sarcomatoid differentiation not described previously in a metastatic Leydig cell tumor.