Mutually exclusive mutations of KIT and RAS are associated with KIT mRNA expression and chromosomal instability in primary intracranial pure germinomas

Abstract

Intracranial germ cell tumors (iGCTs) are the second most common brain tumors among children under 15 in Japan. The pathogenesis of iGCTs is largely unexplored. Although a subset of iGCTs is known to have KIT mutation, its impact on the biology and patients' survival has not been established. In this study, we investigated genes involved in the KIT signaling pathway. 65 iGCTs (30 pure germinomas, 14 teratomas, 18 mixed GCTs, 2 yolk sac tumors, 1 choriocarcinoma) were screened for mutation of KIT, KRAS, NRAS, HRAS, BRAF, PDGFRA, and IDH1 by direct sequencing. KIT expression was examined by immunohistochemistry and quantitative PCR. Chromosomal status was analyzed by array-comparative genomic hybridization (aCGH). Somatic mutations were detected only in KIT and RAS, which were frequently observed in pure germinomas (60.0 %), but rare in non-germinomatous GCTs (NGGCTs) (8.6 %). All KIT/RAS mutations were mutually exclusive. Regardless of the mutation status or mRNA expression, the KIT protein was expressed in all germinomas, while only in 54.3 % of NGGCTs. Amplification of KIT was found in one pure germinoma by aCGH. In pure germinomas, high expression of KIT mRNA was associated with the presence of KIT/RAS alterations and severe chromosomal instability. Our results indicate that alterations of the KIT signaling pathway play an important role in the development of germinomas. Pure germinomas may develop through two distinct pathogeneses: one with KIT/RAS alterations, elevated KIT mRNA expression and severe chromosomal instability, and the other through yet an unidentified mechanism without any of the above abnormalities.

Recurrent neomorphic mutations of MTOR in central nervous system and testicular germ cell tumors may be targeted for therapy

“…We have previously reported in our preliminary study that mutually exclusive mutations of KIT/RAS are found in 60 % of pure germinomas; they are, however, rare among NGGCTs, suggesting that there may be some genetic factors that determine the phenotypical diversity of GCTs [3]. A recent investigation using whole exome sequencing confirmed that mutations of KIT or RAS are the most frequent event in CNS GCTs, as well as identified several other genes including CBL, BCORL1 and MTOR as mutated in a subset of these tumors [24].…”

“…Design of the Ion AmpliSeq primers, Ion Torrent sequencing and the mutation call are described in the Supplementary Information. Selected mutations detected by either WES or Ion Torrent sequencing were confirmed by Sanger sequencing performed as previously described [3].…”

Pineal region tumors: a simplified management scheme

“…Such mutations are mutually exclusive and are positively correlated with KIT mRNA overexpression and chromosomal instability [28]. The importance of these findings is that molecular targeting agents, such as imatinib, which is an inhibitor of specific tyrosine kinases, including KIT, can be used in the management of GGCTs that harbor KIT mutations.…”

“…However, some suggest that patients with these mutations require long-term follow-up due to the risk of secondary GCTs [29]. Similar molecular and genetic findings have not been clearly uncovered in the pathogenesis of NGGCTs [28].…”

“…Further genetic studies are required to understand the pathogenesis of GCTs and subsequently improve the outcomes of these tumors, especially those who fail conventional treatments [28,29,31].…”