GCT-43. GAIN OF SHORT ARM OF CHROMOSOME 12 IS A MOLECULAR MARKER TO PREDICT PROGNOSIS AND REPRESENTS AN EARLY EVENT IN TUMORIGENESIS IN INTRACRANIAL GERM CELL TUMORS

Gain of short arm of chromosome 12 (12p) is commonly observed in testicular germ cell tumors (tGCTs) and also seen in intracranial GCTs (iGCTs). However, little is known about the clinical significance of 12p gain in iGCTs. We have collected over 200 fresh frozen tissue samples of iGCTs through the Intracranial Germ Cell Tumor Genome Analysis Consortium in Japan. Firstly, we analyzed DNA methylation profile in 83 iGCTs, 3 tGCTs (seminomas) and 6 normal control samples using Infinium Human Methylation 450K BeadChip array (Illumina, CA, USA) in order to determine 12p gain status. Then, fluorescence in situ hybridization (FISH) study was carried out on 3 mixed iGCT cases using 12p/CEP12 probe (Abbott Molecular, Abbott park, IL, USA). Lastly, 58 iGCTs with clinicopathological information were analyzed for progression-free survival (PFS) and overall survival (OS). Gain of 12p was observed in 100% (3/3) of seminoma, 14% (3/22) of germinoma, 17% (1/6) of mature teratoma, 25% (1/4) of immature teratoma, 55% (11/20) of mixed germ cell tumor, 100% (4/4) of yolk sac tumor, 100% (1/1) of embryonal carcinoma, and 100% (1/1) of choriocarcinoma. In total, 45% (37/83) of iGCT showed 12p gain. Different histological components in each mixed GCT shared the same 12p copy number status within each mixed GCT case. Both PFS and OS were significantly worse in iGCTs with 12p gain (PFS: P=0.027, OS: P=0.0012). Gain of 12p can be a molecular marker to predict prognosis and represents an early event in tumorigenesis prior to histological differentiation in iGCTs.