Epidemiology and etiology Testicular tumors are rare tumors, accounting for 1% to 1.5% of male tumors and 5% of urological tumors. Its incidence rate has obvious differences in different regions, with the highest in Scandinavia (Denmark and Norway), Switzerland, Germany and New Zealand, the middle in the United States and the United Kingdom, and the lowest in Africa and Asia. There are also marked differences between races, with black Americans being one third as common as white Americans and 10 times as common as black Africans. In Israel, the incidence is at least eight times higher among Jews than among non-Jews. Since the 20th century, there has been a trend toward a gradual increase in global incidence, especially in some Western countries, at a rate of 1% to 2% per year. In the last 40 years, the incidence of testicular tumors has risen by more than a factor of 1 worldwide. In the last 20 years, the number of testicular cancer patients in the United States has increased by 25%, and the incidence of testicular tumors in Canada has even risen by about 50%. 7,920 new cases were reported in the United States in 2007, 95% of which were seminal cell tumors. In the West, there are 3-6 new cases per 100,000 men per year. In China, the incidence rate is about 1/100,000, accounting for 1% to 2% of all malignant tumors in men and 3% to 9% of malignant tumors in the genitourinary system. According to the statistics, the incidence rate of testicular tumor in Beijing urban area from 1993 to 1997 was 0.5/100,000, and that of Shanghai area from 1978 to 1989 was 0.8/100,000, of which the highest was 1.1/100,000 in 1988. Bilateral testicular tumors accounted for 1% to 2%. The majority of cases were germ cell tumors, accounting for 90% to 95%. Germ cell tumors have become the most common solid tumors in men aged 15 to 35 years. The causes of testicular tumors are not well understood, and there are multiple risk factors based on epidemiological analysis. Among the congenital factors are cryptorchidism or undescended testis, familial genetic factors, Klinefelter syndrome, testicular feminization syndrome, polymastia, and estrogen overproduction. Acquired factors are generally thought to be related to injury, infection, occupational and environmental factors, nutritional factors, and excessive application of exogenous estrogen by the mother during pregnancy. Genetic studies have shown that testicular tumors are associated with ectopic short arm of chromosome 12, and alterations in the P53 gene also have a correlation with the development of testicular tumors. In recent years, the survival rate of testicular tumors has changed greatly, from 60% to 65% in the 1960s to more than 90% in the 1990s, and the treatment of testicular tumors has become a successful model for the comprehensive treatment of solid tumors. The increase in the cure rate of testicular tumors relies on correct clinical and pathological staging, advances in imaging and improved detection of serum tumor markers, advances in surgical methods, correct selection of chemotherapy regimens, and advances in radiation therapy. Classification of testicular tumors There are many classification criteria for testicular tumors, and according to the current clinical application, the improved classification criteria specified by the International Health Organization (WHO) in 2004 (Table 1) are recommended. Table 1 Classification criteria designated by the International Health Organization (WHO) in 2004 1. Germ cell tumors Germ cell tumors within the seminiferous tubules Spermatogonial tumors (including those with syncytial trophoblastic cells) Spermatoblastic spermatogonial tumors (note that the spermatoblastic spermatogonial tumors are accompanied by sarcomatous components) Embryonic carcinomas Egg yolk sac tumors (endodermal sinus tumors) Chorionic villus epithelial cancers Teratomas (mature teratomas, immature teratomas, and teratomas with malignant features) Teratomas (mature teratomas, immature teratomas, and teratomas with malignant components) Tumors of more than one tissue type (mixed)-indicate percentage of each component 2. Interstitial Tumors of the Sex Cord/Gonads Mesenchymal Cell Tumors Malignant Mesenchymal Cell Tumors Supporting Cell Tumors Lipid-rich variant Sclerosing type Macrocytic calcific type Malignant Supporting Cell Tumors Granulosa Cell Tumors Adult-type Juvenile type Vesicular cell tumor/fibroblastoma Other gonadal/gonadal mesenchymal tumors Incompletely differentiated type Mixed type Tumors that contain germ cells and gonadal/gonadal mesenchyme (gonoblastomas) 3. Other nonspecific mesenchymal tumors Ovarian epithelial-type tumors Tumors of the collecting ducts and testicular network Nonspecific mesenchymal tumors (benign and malignant)