Testicular neoplasms occur in roughly 6 per 100,000 males. In the 15to 34-year-old age group, when these neoplasms peak in incidence, they are the most common tumors in men. Neoplasms of the testis are heterogeneous and include germ cell tumors and sex cord–stromal tumors. In postpubertal males, 95% of testicular tumors arise from germ cells, and almost all are malignant. By contrast, sex cord-stromal tumors derived from Sertoli or Leydig cells are uncommon and usually benign. The focus of the remainder of this discussion is on testicular germ cell tumors.
The cause of testicular neoplasms is poorly understood. Testicular tumors are more common in whites than in blacks, and the incidence has increased in white populations over recent decades. As discussed earlier, cryptorchidism is associated with a 3to 5-fold increase in the risk for cancer in the undescended testis, as well as an increased risk for cancer in the contralateral descended testis. A history of cryptorchidism is present in approximately 10% of cases of testicular cancer. Intersex syndromes, including androgen insensitivity syndrome and gonadal dysgenesis, also are associated with an increased frequency of testicular cancer. Family history is important, as brothers of males with germ cell tumors have an 8to 10-fold increased risk, presumably owing to inherited factors. The development of cancer in one testis also is associated with a markedly increased risk for neoplasia in the contralateral testis. Extra copies of the short arm of chromosome 12, usually due to the presence of an isochromosome 12 [i(12p)], are found in virtually all germ cell tumors. Of note, point mutations that create oncogenes are relatively rare in germ cell tumors, occurring at the lowest frequency of any solid tumor in adults. Among these are oncogenic mutations in KIT which are found in up to 25% of tumors.
Most testicular tumors in postpubertal males arise from germ cell neoplasia in situ. This precursor lesion is present in conditions associated with a high risk for developing germ cell tumors (e.g., cryptorchidism, dysgenetic gonads) and exhibits the same abnormality of chromosome 12 that is characteristic of fully developed germ cell tumors. As might be expected, germ cell neoplasia in situ often is found in “normal” testis adjacent to full-blown germ cell tumors.
Testicular germ cell tumors are subclassified into seminomas and nonseminomatous germ cell tumors ( 18.1 ). Seminomas are most common, accounting for about http://ebooksmedicine.net
Table 18.1 Summary of Testicular Tumors
Spermatocytic50-60Small,medium,andlargepolygonalcells;noNegativetumor
Yolksactumor3Poorlydifferentiatedendothelium-like,cuboidal,90%ofpatientshaveelevatedAFPorcolumnarcells 50% of testicular germ cell neoplasms. They are histologically identical to tumors called dysgerminomas, which occur in the ovary, and germinomas, which occur in the central nervous system and other extragonadal sites.
MORPHOLOGYGermcelltumorsmaybe“pure”(i.e.,composedofasinglehistologictype)ormixed(seenin40%ofcases).Seminoma presentsasasoft,well-demarcated,gray-whitetumorthatbulgesfromthecutsurfaceoftheaffectedtestis(
Fig.18.3 ).Largetumorsmaycontainfociofcoagulativenecrosis,usuallywithouthemorrhage.Seminomasarecomposedoflarge, uniform cells with distinct cell borders, clear, glycogen-rich cytoplasm, round nuclei, and conspicuous nucleoli (