Definition of Leydig cell tumor:

A Leydig cell tumor is a tumor of the testicle. It develops from Leydig cells -- the cells in the testicles that release the male hormone, testosterone.

Causes, incidence, and risk factors:

The cause of this tumor is unknown. There are no known risk factors for getting this tumor. Unlike germ cell tumors of the testicles, this tumor does not seem to be linked to undescended testes (cryptorchidism).

Leydig cell tumors make up a very small number of all testicular tumors. They are most often found in men between the ages of 20 and 60. This tumor is not common in children before puberty, but it may cause early puberty.