Leydig cell tumours of the testicle are rare. They make up approximately 1% of all testicular tumours.

3 out of 4 Leydig cell tumours occur in adult men. These will usually appear as a swelling on, or enlargement of, one of the testicles. Occasionally they also cause some swelling of the breasts around the nipples (a condition known as gynaecomastia) and loss of sex drive. 1 in every 4 Leydig cell tumours will occur in young boys and these can cause an apparent 'early puberty' with the development of pubic hair, a deepening voice and enlarging genitalia, as well as a testicular swelling. These changes occur because these tumours can produce hormones.

Leydig cell tumours are usually slow growing and the great majority are benign (non-cancerous). This means that an operation to remove the affected testicle (called an orchidectomy) will usually cure the problem.

If it is suspected that the tumour might be cancerous then a bigger operation may be recommended. This would involve taking away some of the lymph nodes in the abdomen. If a tumour is malignant it can spread to the lymph nodes and from there potentially travel to other parts of the body (such as the lungs, liver or bones). The operation to remove the lymph nodes is called a retroperitoneal lymph node dissection and would be done in addition to removing the testicle.

Surgery is the main treatment for these tumours as they are not usually very sensitive to chemotherapy or radiotherapy.