Identification and validation of liquid biopsy-based methylation biomarkers: a germ cell tumor subtype-specific study

Human germ cell tumors (GCTs) occur in infants, children, and adults, and present as germinomatous and/or non-germinomatous (embryonal carcinoma, teratoma, yolk sac tumor (YST), and choriocarcinoma) histologies at gonadal or extragonadal locations. Accurate subtyping is crucial for prognosis and treatment, but current clinical biomarkers lack sensitivity and specificity (serum proteins) or require a tissue biopsy (immunohistochemistry). Hence, less-invasive and improved subtype-specific biomarkers have potential for clinical utility. We conducted a meta-analysis of DNA methylation data (450K/EPIC array) from 15 (three original and 12 published) datasets including 713 GCTs, 109 healthy testis, and 221 healthy peripheral blood samples, revealing that GCT histology is the primary driver of methylation profiles, regardless of tumor location and patients age or sex. Per subtype, we identified differentially methylated regions as potential biomarkers. As proof of concept, we identified and validated two YST-specific biomarkers, i.e., APC and DPP7 promotor methylation, using methylation-sensitive restriction enzyme-based qPCR, of which DPP7 was also detectable in GCT serum-derived cell-free DNA. In conclusion, we present a novel method for in silico identification and in vitro and in vivo validation of YST subtype-specific liquid biopsy-based biomarkers. Our bioinformatic pipeline is easily transferrable encouraging additional applications in pan(pediatric)-cancer studies beyond GCTs.