PRACTICAL UROPATHOLOGY Urol Sci 2010;21(1):55-57 ©2010 Taiwan Urological Association. Published by Elsevier Taiwan LLC. 55 Histopathology and Biology of Testicular Germ Cell Tumor Chin-Chen Pan* Department of Pathology, Taipei Veterans General Hospital and National Yang-Ming University, Taiwan 1. Introduction The versatile histopathology, clinical presentation, and bi- ologic behavior of testicular neoplasms reflect the com- plex composition of the male gonad. Each component can develop different tumor types; thus, there are testicular germ cell tumor (TGT), sex cord/stromal tumor, miscel- laneous tumors arising from rete testis or paratesticular structures, and tumors not specific to testicular paren- chyma, such as lymphoma or mesenchymal neoplasms. All these varieties pose a challenge to both pathologists and clinicians regarding their diagnosis and treatment. 2. Nomenclature Nowadays, the most widely adopted classification is the 2004 World Health Organization (WHO) classification. 1 The terminology of the 2004 WHO classification is essentially the same as the classification for ovarian tu- mors. However, one should bear in mind that the clin- icopathologic features of testicular tumors are markedly different from those of ovarian tumors. Other than the WHO classification, there are other terms that are no longer in use, such as “infantile embryo- nal carcinoma”, which refers to pediatric yolk sac tumor, and “endodermal sinus tumor”, which is also equivalent to yolk sac tumor. In 1976, a divergent classification was pro- posed by the British Testicular Tumor Panel, which intended to call most TGT as teratoma. 2 However, the classification did not gain worldwide acceptance. 3. Relevance of Histopathologic Classification The histopathologic classification of TGT is strongly as- sociated with clinical features. In terms of age distribution, the incidence shows three age groups. In the infants and children, the majority of TGT are composed of yolk sac tumor and teratoma. In young adults in the third to fourth decade, seminoma and mixed germ cell tumors predom- inate. Testicular tumors in men older than 50 years have a high frequency of malignant lymphoma. Spermatocytic seminoma is a rare tumor, and almost all occurs in the elderly. 3 The histologic subtypes also reflect the degree of dif- ferentiation and correlate with biologic behavior in respect to benignity versus malignancy. In the pediatric group, yolk sac tumor is malignant while all prepubertal testicu- lar teratomas are benign even with immature histology. On the contrary, all postpubertal TGTs are malignant, even those with “benign” histology (mature teratoma) still have metastatic potential. 4 The teratoma is considered the most differentiated form, while the embryonal carcinoma the most dedifferentiated one. Hence, the proportion of dif- ferent elements may influence the overall prognosis. 5,6 The different forms also dictate their metastatic route. Most of the TGT components metastasize to retroperito- neal lymph nodes through lymphatics; 7 meanwhile, the choriocarcinoma is notorious for its hematogenous spread owing to its propensity to invade vascular system even when the tumor is small. Therefore, choriocarcinoma can skip the retroperitoneal lymph nodes before it de- velops widespread metastases. 8 Accepted: January 11, 2010 *Corresponding author. Department of Pathology, Taipei Veterans General Hospital, 201, Shi-Pai Road, Section 2, Taipei 11217, Taiwan. E-mail: ccpan@vghtpe.gov.tw CORE Metadata, citation and similar papers at core.ac.uk Provided by Elsevier - Publisher Connector