Intracranial germ cell tumors (IGCTs) are a group of rare heterogeneous brain tumors which are clinically and histologically similar to the more common gonadal GCTs.
IGCTs show great variation in their geographic and gender distribution, histological composition and treatment outcomes. The incidence of IGCTs is historically 5-8 fold greater in Japan and other East Asian countries than in Western countries with peak incidence near the time of puberty.
About half of the tumors are located in the pineal region. The male-to-female incidence ratio is approximately 3-4:1 overall but even higher for tumors located in the pineal region.
Due to the scarcity of tumor specimens available for research, little is currently known about this rare disease.
With a worldwide collaboration with multiple research institutes, we analyzed 62 cases by next generation sequencing, SNP array and expression array. We find the KIT/RAS signaling pathway frequently mutated in over 50% of IGCTs including novel recurrent somatic mutations in KIT, its downstream mediators KRAS and NRAS, and its negative regulator CBL. Novel somatic alterations in the AKT/mTOR pathway included copy number gain of the AKT1 locus at 14q32.33 in 19% of patients, with corresponding upregulation of AKT1 expression. We identified loss-of-function mutations in BCORL1, a transcriptional corepressor and tumor suppressor. We report significant enrichment of novel and rare germline variants in JMJD1C, a histone demethylase and coactivator of the androgen receptor, among Japanese IGCT patients.
This study establishes a molecular foundation for understanding the biology of IGCTs and suggests potentially promising therapeutic strategies focusing on the inhibition of KIT/RAS activation and the AKT1/mTOR pathway.