Orchiectomy is the surgical removal of one or both testicles, or testes. This procedure is done to treat cancer, or to lower the level of testosterone. Surgical removal of a testicle is the usual treatment if a tumor is found within the gland itself, but an orchiectomy may also be performed to treat prostate cancer or cancer of the male breast, as testosterone causes these cancers to grow and metastasize (spread to other parts of the body).