Testicular tumors in children are rare, accounting for only 1-2% of all solid tumors in this age group.  In both children and adults, the vast majority of testis tumors arise from germ cells. Seminoma is a type of testicular germ cell tumor that is believed to originate from the germinal epithelium of the seminiferous tubules. Recently, these tumors have been shown to have dramatic sensitivity to both radiotherapy and cytotoxic chemotherapy. In most patients with testicular tumors (including seminoma), the disease is readily cured with minimal long-term morbidity. The management of childhood seminoma is similar to that of adult seminoma.
Germ cell tumors account for 95% of testicular tumors and include seminomas, teratomas, choriocarcinomas, and mixed tumors. Seminomas comprise approximately 50% of all germ cell tumors. Seminomas are generally believed to arise from the germinal epithelium of the seminiferous tubules because "seminoma cells" are morphologically similar to spermatogonia and also because seminomas are frequently found within the seminiferous tubules in early stages.
Most researchers believe that seminomas can arise from any or all of the spermatocytic elements because undifferentiated seminomas can resemble primordial germ cells, spermatogonia, or spermatocytes. Unlike the nonseminomatous germ cell tumors, pure seminoma tends to remain localized or tends to involve only lymph nodes. Seminoma is confined to the testis in 85% of patients at presentation. It initially spreads to draining lymph nodes in the retroperitoneum and then spreads proximally to involve the next echelon of draining lymphatics in the mediastinum and supraclavicular fossa. Only rarely does pure seminoma spread hematogenously to involve lung parenchyma, bone, liver, or brain (ie, stage IV). Less than 5% of patients present with stage III or stage IV disease. 
Germ cell tumors are the most common solid tumor in men aged 15-35 years.  The worldwide incidence has more than doubled over the past 40 years, and approximately 7500 cases are diagnosed annually in the United States. Seminomas account for nearly 50% of these cases.
With recent advances in radiologic staging, serum tumor marker surveillance, and platinum-based chemotherapy for advanced disease, overall survival (ie, cure) rates for patients with seminoma have increased to more than 90%. Nearly 100% of patients with stage I testicular seminoma are cured. Potential adverse effects/morbidity related to therapy for this malignancy are discussed below; in general, morbidity includes infertility, second cancers, chemotherapy-related nausea and vomiting, nephrotoxicity, and cardiovascular toxicity or peptic ulcer disease from mediastinal or retroperitoneal irradiation, respectively.
Geographic distribution of testicular cancer widely varies, with the highest rates among North American whites, Scandinavians, and Western Europeans. The lowest rates occur among Asians, Africans, Puerto Ricans, and North American blacks. Recent data show a white-to-black incidence ratio of approximately 5:1, and a report from the US military showed a relative white-to-black incidence ratio of 40:1.
In children and adolescents, the pattern of racial distribution for testicular cancer is different. A review of the Surveillance, Epidemiology, and End Results (SEER) data from 1973-2000 reported that Asians and Pacific Islanders had the highest incidence of testicular cancer at 7.6 per million, whereas American Indians and Alaskan Natives had an incidence of 1.4 per million children. The rates for Caucasian and African American children were the same at 5.1 per million. 
Seminomas arise from the male testicle.
As noted above, germ cell tumors are the most common solid tumors in men aged 15-35 years. Seminoma (the most common germ cell tumor) occurs most commonly in the fourth decade of life. Children represent only 2-5% of all patients with testicular cancer. Seminoma is considered a postpubertal tumor, although it has been reported in a patient as young as 8 years.
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