Primary and recurrent diffuse astrocytomas: genomic profile comparison reveals acquisition of biologically relevant aberrations

Abstract

Background: Diffuse astrocytomas are characterized by their highly variable biological behavior. The possibility that tumors develop novel aberrations, with relevant biological properties, is often neglected. In this study, we present two cases of diffuse astrocytoma in which additional cytogenetic and epigenetic markers with potential influence on cell proliferation or differentiation were detected at relapse.

Findings: The biopsies taken from the primary and recurrent tumors of two patients were analyzed with molecular methods to detect copy number variations (CNVs), gene mutations and epigenetic changes. Both cases were characterized by the R132H mutation in the isocitrate dehydrogenase 1 (IDH1) gene. Features typical of astrocytomas, such as copy-neutral loss of heterozygosity at 17p and the deletion of the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene, were also detected in both cases. These markers were present in the primary and recurrent lesions. Other aberrations, predominantly deletions or amplifications of chromosomal segments and the hypermethylation of gene promoters, were detected in the recurrent lesions.

Conclusions: The IDH1 mutation was the primary event, as previously reported. According to our observations, the methylation of promoters constituted later events, which may have further disrupted cell proliferation and/or differentiation, together with additional CNVs.

Keywords: Clonality; Diffuse astrocytoma; Isocitrate dehydrogenase 1; MutL homolog 3.

Fig. 1

Time line representing the dates of resection and the type of treatment the case no. 1 received

Fig. 2

Molecular cytogenetic and epigenetic analyses of the three lesions of case no. 1. a Results of a SNP array for each lesion, with the selection of three chromosomes, in which additional changes were detected. Red bars indicate deletions of a chromosomal region. Green bars represent amplifications, and CN-LOH is marked with gray boxes. b Result of I-FISH analysis confirming and extending the SNP array findings. 1,3, deletion of 19q13 probe; 2, amplification of 13q34; 4, multiple amplifications of 13q34 probe; 5, amplification of 13q34 with monoallelic loss of the RB1 gene; and 6, trisomy of chromosome 7

Fig. 3

Time line representing the dates of resection and the type of treatment the case no. 2 received

Fig. 4

Molecular cytogenetic and epigenetic analyses of the three lesions of case no. 2. a Results of the SNP array for each lesion, with the selection of three chromosomes, in which the additional changes were detected. Red bars indicate the deletion of a chromosomal region. Green bars represent amplifications, and CN-LOH is marked with gray boxes. b Results of I-FISH analysis confirming and extending the SNP array findings. 1, biallelic deletion of subtelomeric area of the long arm of chromosome 6; 2, biallelic deletion of the CDKN2A gene; 3, deletion of the PTEN gene in polyploid nuclei; 4, the RB1 gene and 13q34 were not affected by chromothripsis

Fig. 5

Verification of MLH3 promoter methylation by MS-PCR. Three sets of primers designed to recognize unconverted DNA (W primers), converted unmethylated DNA (U primers), and converted methylated DNA (M primers) were used for each bisulfite-treated DNA