Testicular cancer is the most common solid tumor in men between the ages of 20 and 35 years. There are three modal peaks: infancy, ages 25 to 40, and about age 60.
A solid testicular mass in a man aged 50 or greater is usually a lymphoma. An estimated 6000 new cases and 350 deaths due to testicle cancer occured in the United States in 1995. The lifetime probability of developing a GCT is approximately 0.2% for an American Caucasian male. The incidence of testis cancer varies significantly according to geographic area. The reported incidence is highest in Scandinavia, Switzerland, Germany, and New Zealand; intermediate in the United States and Great Britain; and lowest in Africa and Asia. The worldwide incidence of testis GCT has more than doubled in the past 40 years.
GCTs are seen principally in young Caucasians, rarely in African-Americans. The published ratio between Caucasian and African-American patients is approximately 4 to 5:1, although it was closer to 40:1 ratio in the US Military. In African-Americans, GCT behaves similarly to that of the general population, and the incidence of GCT in African-Americans has not increased over the past 40 years. Familial clustering has been observed, particularly among siblings.
The cause of GCT is unknown. Hypotheses implicating an endocrine-driven, pituitary stimulation of damaged germinal epithelium have not been proved. Instead, random genetic events occurring during the early stages of meiosis seem to be responsible for the malignant transformation of germ cells (see section on biology). A few congenital developmental defects predispose to the disease.
The risk of GCT occurring in the cryptorchid testis is several times the risk in normally descended testes. Between 5% and 20% of patients with a history of cryptorchidism develop a tumor in the normally descended testis.An abdominal cryptorchid testis is more likely to develop GCT than an inguinal cryptorchid testis. The protective effect of orchiopexy is difficult to quantify, but most data suggest a reduced likelihood of GCT if orchiopexy is performed prior to puberty. If the testis is inguinal, hormonally functioning, and easily examined, surveillance is recommended. If the testis is not amenable to orchiopexy or cannot be adequately examined, orchiectomy is recommended.