No abstract

Background Glioblastoma (GBM) is the most common and aggressive form of glioma. GBM frequently displays chromosome (chr) 7 gain, chr 10 loss and/or EGFR amplification (chr7+/chr10-/EGFRamp). Overall survival (OS) is 15 months after treatment. In young adults, IDH1/2 mutations are associated with longer survival. In children, histone H3 mutations portend a dismal prognosis. Novel reliable prognostic markers are needed in GBM. We assessed the prognostic value of mitochondrial DNA (mtDNA) copy number in adult GBM. Methods mtDNA copy number was assessed using real-time quantitative PCR in 232 primary GBM. Methylation of POLG and TFAM genes, involved in mtDNA replication, was assessed by bisulfite-pyrosequencing in 44 and 51 cases, respectively. Results Median age at diagnosis was 56.6 years-old and median OS, 13.3 months. 153/232 GBM (66 %) displayed chr7+/chr10-/EGFRamp, 23 (9.9 %) IDH1/2 mutation, 3 (1.3 %) H3 mutation and 53 (22.8 %) no key genetic alterations. GBM were divided into two groups, “Low” (n = 116) and “High” (n = 116), according to the median mtDNA/nuclear DNA ratio (237.7). There was no significant difference in OS between the two groups. By dividing the whole cohort according to the median age at diagnosis, OS was longer in the “High” vs “Low” subgroup (27.3 vs 15 months, p = 0.0203) in young adult GBM (n = 117) and longer in the “Low” vs “High” subgroup (14.5 vs 10.2 months, p = 0.0116) in older adult GBM (n = 115). POLG was highly methylated, whereas TFAM remained unmethylated. Conclusion mtDNA copy number may be a novel prognostic biomarker in GBM, its impact depending on age.

Ein 74-jähriger Mann mit Fitzpatrick-Hauttyp II stellte sich wegen einer dunklen Hautveränderung auf dem Rücken vor. Nach Angaben des Patienten sei der dunkle Fleck vor etwa 10 Jahren aufgetaucht und habe sich seitdem nicht verändert. Bei der klinischen Untersuchung fiel ein asymptomatischer bräunlicher, unregelmäßig begrenzter, etwa 10 cm x 6 cm großer Fleck auf dem oberen Rücken auf. In seiner Nähe befand sich ein Lipom (Abbildung 1). Die weitere körperliche Untersuchung war unauffällig.

Young patients (< 40 years-old) with glioblastoma (GB) may carry IDH1/2 mutations or rarely, H3F3A/HIST1H3B mutations. Some instead harbor chromosome (chr) 7 gain, chr 10 loss, and EGFR amplification (amp). IDH1/2 mutations are associated with longer survival in contrast to H3F3A/HIST1H3B mutations. Novel reliable prognostic factors are needed in GB. Mitochondria (mt) are responsible for ATP production through oxidative phosphorylation. High mtDNA copy number (CN) has been associated with variable outcomes in cancer. The mtDNA-CN was assessed by RT Q-PCR in 66 GB from patients 18 to 40 years-old. Whole mitochondrial genome sequencing was performed in 18/66 GB. 17/66 (25.8%) cases harbored IDH1-R132H mutation; 29/66 (44%) had chr 7 gain/chr 10 loss and/or EGFRamp; 4/66 (6%) harbored H3F3A/HIST1H3B mutations. The remaining cases (24.2%) had no key genetic alterations. The mtDNA/nuclearDNA ratio was subdivided into groups: Low and High according to the median (mtDNA-CN median 194.9). 33 patients displayed a low ratio (≤ median) whereas 33 displayed a high ratio (> median). The overall survival in the High vs Low group was significantly longer in the whole cohort (Log-rank test, 31.8 vs 14.2 months, p= 0.019) and the chr7+/chr10-/EGFRamp subgroup (37.8 vs 12.1 months; p= 0.0117). There was still a trend towards longer survival in the High vs Low group within the other genetic subgroups (IDH-mutant; no genetic alteration) except for the H3-mutant GB (4 patients). Analyses on 232 patients 18 to 84 years-old showed that among patients < 56 years-old, the High group (58 cases) had a longer survival compared to the Low group (59 cases) (27.3 vs 15 months; p= 0.023). High mtDNA level is linked to oxidative metabolism (which decreases tumor aggressiveness) and cell differentiation. Increasing mtDNA-CN might induce tumor cell differentiation and slow disease progression. In conclusion, mtDNA-CN may be a novel prognostic biomarker in GB.