Abstract
9506 Background: Medulloblastoma is the most common malignant brain tumor and a significant cause of cancer mortality in children. Despite considerable therapeutic advances, prognosis remains poor, with a five-year-survival rate of about 60% emphasizing the urgent need for markers to allow for a more accurate tailoring of treatment intensity. Methods: We performed genome-wide analysis of DNA-copy number in 112 medulloblastomas using array-CGH. All patients had received craniospinal irradiation after surgery. Standard adjuvant chemotherapy with lomustine, cisplatin and vincristine or a regimen with equal potency had been administered to 73 patients. To identify novel prognostic markers, DNA copy number information was correlated with survival data using log rank and chi-square tests. For selected candidate genes identified by array-CGH, mRNA and protein expression were analyzed by real-time quantitative PCR, and immunohistochemically on tissue microarrays consisting of medulloblastomas from 189 patients. Results: Copy-number gains of chromosomes 6 and 17q, high-level amplifications of MYC and MYCN, and loss of 9p21.3 (CDKN2A locus) were identified as significant adverse prognostic markers; monosomy 6 was associated with good prognosis. Monosomy 6 and gain of 17q were mutually exclusive, whereas trisomy 6 almost always occurred in conjunction with 17q gain. Tumors with trisomy 6 and 17q gains exhibit strong up-regulation of MAP3K7 (chr. 6) and NLK (17q) mRNA, two key-enzymes of the non-canonical calcium-dependent Wnt-signaling pathway. Furthermore, this subgroup exclusively shows high mRNA-expression of several cancer-retina antigens (e.g. GNGT1, GNGT2, PDE6, RCV1, RDS and NRL). Tumors with monosomy 6, in contrast, display highly activated canonical Wnt signaling as indicated by nuclear protein expression of beta-catenin. Conclusions: We propose a model for the molecular risk stratification of medulloblastoma comprising five risk groups with significantly different survival using copy-number status of MYC, MYCN, and chromosomes 6 and 17q. Furthermore, we give evidence for a role of noncanonical calcium-dependent Wnt-signalling in medulloblastoma metastasis in a subset of tumors. Cancer-retina antigens could be used to facilitate the diagnosis and follow-up of this molecular subgroup. No significant financial relationships to disclose.
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