Germ Cell Tumors of the Testis
Epidemiology and Risk Factors
Malignant tumors of the testis are rare, with approximately 9 new cases per 100,000 males reported in the United States each year. Of all primary testicular tumors, 90–95% are germ cell tumors (seminoma and nonseminoma), while the remainders are nongerminal neoplasms (Leydig cell, Sertoli cell, gonadoblastoma). The lifetime probability of developing testicular cancer is 0.2% for a white male in the United States. Survival of patients with testicular cancer has improved dramatically in recent years, reflecting the development and refinement of effective combination chemotherapy. Of the 8480 new cases of testicular cancer in the United States in 2010, only 350 deaths are expected.
The incidence of testicular cancer shows marked variation among different countries, races, and socioeconomic classes. Scandinavian countries report up to 6.7 new cases per 100,000 males annually; Japan reports 0.8 per 100,000 males. In the United States, the incidence of testicular cancer in blacks is approximately one-fourth that in whites. Within a given race, individuals in the higher socioeconomic classes have approximately twice the incidence of those in the lower classes.
Testicular cancer is slightly more common on the right side than on the left, which parallels the increased incidence of cryptorchidism on the right side. Of primary testicular tumors, 1–2% are bilateral, and about 50% of these tumors occur in men with a history of unilateral or bilateral cryptorchidism. Primary bilateral tumors of the testis may happen synchronously or asynchronously but tend to be of the same histologic type. Seminoma is the most common germ cell tumor in bilateral primary testicular tumors, while malignant lymphoma is the most common bilateral tumor of the testis.
Although the cause of testicular cancer is unknown, both congenital and acquired factors have been associated with tumor development. The strongest association has been with the cryptorchid testis. Approximately 7–10% of testicular tumors develop in patients who have a history of cryptorchidism; seminoma is the most common form of tumor these patients have. However, 5–10% of testicular tumors occur in the contralateral, normally descended testis. The relative risk of malignancy is highest for the intra-abdominal testis (1 in 20) and is significantly lower for the inguinal testis (1 in 80). Placement of the cryptorchid testis into the scrotum (orchiopexy) lowers the risk of malignancy if it is performed prior to the age of 13 (Pettersson et al, 2007).
Exogenous estrogen administration to the mother during pregnancy has been associated with an increased relative risk for testicular tumors in the fetus, ranging from 2.8 to 5.3 over the expected incidence. Other acquired factors such as trauma and infection-related testicular atrophy have been associated with testicular tumors; however, a causal relationship has not been established.
Numerous classification systems have been proposed for germ cell tumors of the testis. Classification by histologic ...