[Germ Cell Tumours of the Testis: Classification, Frozen Section Diagnostics, Sentinel Lymph Node Biopsy, and Special Biological Variants].

Germ cell tumours (GCTs) are the most common testicular neoplasms and are classified into type I, type II, and type III tumours depending on age of onset, molecular biology, and histomorphology. There are six histological subtypes, whose distribution varies among the three groups: seminomas, embryonal carcinomas, choriocarcinomas, yolk-sac tumours, teratomas, and spermatocytic tumours. The most common are malignant type II GCTs, typically treated with radical orchiectomy. In cases of small tumours where tumour dignity is uncertain - such as when serum markers are negative - initial enucleation followed by frozen section examination can be performed. This approach is particularly useful when benign tumours are suspected, including epidermal cysts, sex cord gonadal stromal tumours, adenomatoid tumours, or other testicular adnexal tumours, since testis-sparing tumour resection is sufficient for small benign tumours. The precise classification of GCTs is based on the histopathological assessment of morphological characteristics of the GCT subtypes and, in certain cases, is supplemented by immunohistochemical analyses. When examining resected specimens from metastatic sites (e.g., retroperitoneal lymph nodes), special biological variants of type II tumours, such as somatic malignancies or the so-called growing teratoma syndrome, may also be encountered. If somatic malignancies lack the characteristic histomorphological features of the typical GCT subtypes, the GCT origin can be confirmed molecular-pathologically by detecting isochromosome 12p or an amplification of chromosomal material on chromosome 12.