Detection of Circulating Tumor Cells (CTCs) in Patients with Testicular Germ Cell Tumors

While the majority of patients with advanced testicular germ cell tumors (GCT) achieve complete responses after chemotherapy and if indicated after postchemotherapy resection of residual lesions, about 20% of patients have incomplete responses or show relapses. Moreover, toxicity of chemotherapy is high, and severe adverse chronic effects have been described. Therefore, there is an urgent need for biomarkers that could help to improve tumor staging, and support decision-making, ideally including monitoring of therapy response and prediction of relapse. Besides the well-established serum markers lactate dehydrogenase, α-fetoprotein, and β-subunit of human chorionic gonadotropin, during recent years new noninvasive liquid biopsy markers have been investigated in GCT, including cell-free nucleic acids like microRNAs, and circulating tumor cells (CTCs).Prognostic relevance has been demonstrated for circulating tumor cells (CTCs) in patients with different cancers. However, little is known in GCT patients. Histologically, GCT are a very heterogeneous group of tumors comprising pure seminomas (consisting of cells that remember primordial germ cells) and nonseminomas, which are either undifferentiated (embryonal carcinoma) or differentiated, exhibiting different degrees of embryonic (teratoma) or extraembryonic (yolk sac tumor and choriocarcinoma) differentiation. This heterogeneity hampers capture and detection of CTCs deriving from those tumors using a single method or a single antibody. To date, label-independent capture methods that enrich tumor cells according to the density of GCT cells, which is similar to that of mononuclear cells, have been successfully applied. Since testicular GCT might also express epithelial proteins, methods based on enrichment of CTCs using epithelial markers are promising to detect CTCs in certain subgroups of patients with GCTs as well.Here, we describe and discuss a combination of methods to capture and detect GCT cells with epithelial and germ cell characteristics in blood.