A t(1;19)(q10;p10) mediates the combined deletions of 1p and 19q and predicts a better prognosis of patients with oligodendroglioma

Identification of genomic aberrations associated with shorter overall survival in patients with oligodendroglial tumors

Deletions on chromosomes 1p and 19q are associated with favorable prognosis in patients with oligodendroglial tumors. The aim of our study was to identify additional genomic aberrations linked to patient survival. We performed a genome-wide screen for genomic imbalances by comparative genomic hybridization on tumors from 70 patients, including 40 oligodendrogliomas, 30 oligoastrocytomas (21 WHO grade II tumors, 49 WHO grade III tumors). Data were correlated with overall patient survival (OS, median follow-up: 5.8 years). The most frequent aberrations were losses on chromosome 19q (64%), 1p (59%), 9p (26%), 4q (21%), 10q (19%), 18q (17%); gains on 7q (24%), 19p (19%), 7p (17%). In univariate analyses, combined 1p/19q and 19q loss were significantly associated with longer OS, and gains on 7, 8q, 19q, 20, losses on 9p, 10, 18q, Xp with shorter OS. Multivariate analyses showed the most significant prognostic factors for OS of patients with any oligodendroglial tumor to be WHO grade [odds ratio (OR) 8], 7p gain (OR 6), 9p loss (OR 3); for OS of patients with anaplastic tumors to be 7p gain (OR 10), 8q gain (OR 5), 18q loss (OR 3). Patients with anaplastic oligodendroglial tumors containing one or more prognostically unfavorable genomic aberration had a poor outcome independent of the 1p/19q status. In summary, we identified several independent genomic markers of shorter survival in patients with oligodendroglial tumors. Thus, molecular diagnostic testing, which is usually restricted to 1p/19q deletion analysis, may need to be refined by additionally assessing the prognostically unfavorable genomic aberrations identified.

Hypermethylation and transcriptional downregulation of the CITED4 gene at 1p34.2 in oligodendroglial tumours with allelic losses on 1p and 19q

Deletions of chromosomal arms 1p and 19q are frequent in oligodendroglial tumours and have been associated with sensitivity to radio- and chemotherapy as well as favourable prognosis. By using microarray-based expression profiling, we found that oligodendroglial tumours with 1p and 19q losses showed significantly lower expression of the CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 4 gene (CITED4) at 1p34.2 as compared to tumours without 1p and 19q losses. Mutational analysis showed no CITED4 mutations in gliomas. However, 1p and 19q losses as well as low expression of CITED4 transcripts were significantly associated with hypermethylation of the CITED4-associated CpG island. In line with the latter finding, treatment of CITED4 hypermethylated glioma cell lines with 5-aza-2'-deoxycytidine and trichostatine A resulted in a marked increase of the CITED4 transcript levels. Furthermore, CITED4 hypermethylation was significantly associated with longer recurrence-free and overall survival of patients with oligodendroglial tumours. Taken together, our results indicate that CITED4 is epigenetically silenced in the vast majority of oligodendroglial tumours with 1p and 19q deletions and suggest CITED4 hypermethylation as a novel prognostic marker in oligodendroglioma patients.