Abstract
Chordomas are rare mesenchymal tumors occurring exclusively in the midline from clivus to sacrum. Early tumor detection is extremely important as these tumors are resistant to chemotherapy and irradiation. Despite continuous research efforts surgical excision remains the main treatment option. Because of the often challenging anatomic location early detection is important to enable complete tumor resection and to reduce the high incidence of local recurrences. The aim of this study was to explore whether DNA methylation, a well known epigenetic marker, may play a role in chordoma development and if hypermethylation of specific CpG islands may serve as potential biomarkers correlated with SNP analyses in chordoma. The study was performed on tumor samples from ten chordoma patients. We found significant genomic instability by Affymetrix 6.0. It was interesting to see that all chordomas showed a loss of 3q26.32 (PIK 3CA) and 3q27.3 (BCL6) thus underlining the potential importance of the PI3K pathway in chordoma development. By using the AITCpG360 methylation assay we elucidated 20 genes which were hyper/hypomethylated compared to normal blood. The most promising candidates were nine hyper/hypomethylated genes C3, XIST, TACSTD2, FMR1, HIC1, RARB, DLEC1, KL, and RASSF1. In summary, we have shown that chordomas are characterized by a significant genomic instability and furthermore we demonstrated a characteristic DNA methylation pattern. These findings add new insights into chordoma development, diagnosis and potential new treatment options.
Highlights
Chordomas are malignant tumors with a phenotype that recapitulates the notochord
Ten chordoma samples were tested for copy number (CN) and LOH using Affymetrix 6.0 copy number variation (CNV)/single nucleotide polymorphisms (SNP) Arrays
Copy numbers were matched with methylation data and presented in Figure 2 to see whether a chromosome is affected by CN-variation or hyper/hypo methylation pattern
Summary
Chordomas are malignant tumors with a phenotype that recapitulates the notochord. These tumors arise within the bones of the axial skeleton and show a destructive growth [1,2]. Chordomas harbor common chromosomal gains and losses [4] they lack balanced or unbalanced chromosomal exchanges. Those lead to the creation of fusion genes and screening for mutations in brachyury (a nuclear transcription factor highly expressed in chordomas) and other common cancer associated genes like KRAS and BRAF which failed to show a consistent genetic profile. DNA methylation is a tightly regulated process during normal development and it becomes deregulated during neoplastic transformation and disease development [5]
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