GERMLINE AND SOMATIC MUTATIONS IN PEDIATRIC GERM CELL TUMORS

Abstract Pediatric germ cell tumors (pGCTs), a group of germ-cell-originated neoplasms, currently lack sufficient study. Although somatic activation of KIT/AKT and RAS/MAPK pathways have been revealed, no driver mutations have been detected in most of GCT cases. To extensively explore germline and somatic mutations, we analyzed genomic and/or transcriptomic sequencing data of 236 pGCTs, including data from not only public datasets but also newly collected whole-genome-sequencing data of tumor samples together with case-unaffected-parents trios collected in Shanghai Xinhua Hospital. A new computational pipeline was developed and carried out to identify functional germline and somatic variants. Overall, > 30,000 germline and > 100,000 somatic mutations were detected and prioritized. Particularly, we found germline trisomy 21 in three cases, germline XXY in five cases, and one germline XO, demonstrating the enrichment of germline chromosomal abnormality in pGCTs (p-value < 0.0001). We identified 196 loss-of-function-like inherited germline mutations involving CBL (4/212), PTEN (3/212), TEX11 (2/212), and ATM (1/212). In addition, we detected 2,160 de novo germline mutations (DNMs), and showed an average of 69.7 DNMs per proband, which is compatible to the previously reported incidence. Moreover, we discovered recurrent somatic mutations in known driver genes such as KIT (27/110), KRAS (10/110), NRAS (4/110), MTOR (5/110), PTEN (3/110), and CBL (2/110). Interestingly, somatic hotspot RRAS2 mutations were detected in seven of 110 cases. Subsequent clinical association analysis showed that patients who harbored RRAS2 mutations were younger than those harboring KRAS mutations (p-value < 0.05). Somatic copy number changes were frequently observed, including chr12p+ (47/110), chr21q+ (47/110), chrX+ (34/110), chr13q- (27/110), and chr20q+ (26/110). Furthermore, we identified chromoplexy in nine out of 62 cases, and this alteration is significantly enriched in yolk sac tumors with the occurrence 7/11. Collectively, portraying the mutational landscape of pGCTs, we revealed its disease etiology and potential new drug targets.