Leydig cell tumor of the testis. Light micrograph (LM) of a section from an affected testis. Leydig cell tumours develop from Leydig cells. These are the cells in the testicles that release the male hormone, testosterone. 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. Testicular cancer is one of the most treatable and curable cancers. This photomicrograph shows sheets of large polygonal cells of the tumour in the right of the image with normal testis in the left of the image. Magnification: x120 when printed at 10 centimetres wide. Human tissue.