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Gliosarcoma is a rare glioblastoma variant characterized by a biphasic tissue pattern with alternating areas that display either glial (glial fibrillary acidic protein–positive) or mesenchymal (reticulin-positive) differentiation. Previous analyses have shown identical genetic alterations in glial and mesenchymal tumor areas, suggesting that gliosarcomas are genetically monoclonal, and mesenchymal differentiation was considered to reflect the elevated genomic instability of glioblastomas. In the present study, we compared genome-wide chromosomal imbalances using array comparative genomic hybridization in glial and mesenchymal tumor areas of 13 gliosarcomas. The patterns of gain and loss were similar, except that the gain at 13q13.3-q14.1 (log2ratio 3.0), containing the STOML3, FREM2, and LHFPgenes, which was restricted to the mesenchymal tumor area of a gliosarcoma. Further analyses of 64 cases of gliosarcoma using quantitative PCR showed amplification of the STOML3, FREM2, and LHFPgenes in 14 (22%), 10 (16%), and 7 (11%) mesenchymal tumor areas, respectively, but not in glial tumor areas. Results of IHC analysis confirmed that overexpression of STOML3 and FREM2 was more extensive in mesenchymal than in glial tumor areas. These results suggest that the mesenchymal components in a small fraction of gliosarcomas may be derived from glial cells with additional genetic alterations.

The current World Health Organization classification recognizes three histological types of grade II low-grade diffuse glioma (diffuse astrocytoma, oligoastrocytoma, and oligodendroglioma). However, the diagnostic criteria, in particular for oligoastrocytoma, are highly subjective. The aim of our study was to establish genetic profiles for diffuse gliomas and to estimate their predictive impact. In this study, we screened 360 World Health Organization grade II gliomas for mutations in the IDH1, IDH2, and TP53genes and for 1p/19q loss and correlated these with clinical outcome. Most tumors (86%) were characterized genetically by TP53mutation plus IDH1/2mutation (32%), 1p/19q loss plus IDH1/2mutation (37%), or IDH1/2mutation only (17%). TP53mutations only or 1p/19q loss only was rare (2 and 3%, respectively). The median survival of patients with TP53mutation ± IDH1/2mutation was significantly shorter than that of patients with 1p/19q loss ± IDH1/2mutation (51.8 months vs.58.7 months, respectively; P= 0.0037). Multivariate analysis with adjustment for age and treatment confirmed these results (P= 0.0087) and also revealed that TP53mutation is a significant prognostic marker for shorter survival (P= 0.0005) and 1p/19q loss for longer survival (P= 0.0002), while IDH1/2mutations are not prognostic (P= 0.8737). The molecular classification on the basis of IDH1/2mutation, TP53mutation, and 1p/19q loss has power similar to histological classification and avoids the ambiguity inherent to the diagnosis of oligoastrocytoma.

Schwannomas are benign nerve sheath tumors composed of well-differentiated Schwann cells. Other than frequent NF2 (neurofibromatosis type 2) mutations (50%–60%), their molecular pathogenesis is not fully understood. LATS1 and LATS2 are downstream molecules of NF2 and are negative regulators of the yes-associated protein (YAP) oncogene in the Hippo signaling pathway. We assessed mutations of the NF2, LATS1, and LATS2 genes, promoter methylation of LATS1 and LATS2, and expression of YAP and phosphorylated YAP in 82 cases of sporadic schwannomas. Targeted sequencing using the Ion Torrent Proton instrument revealed NF2 mutations in 45 cases (55%), LATS1 mutations in 2 cases (2%), and LATS2 mutations in 1 case (1%) of schwannoma. Methylation-specific polymerase chain reaction showed promoter methylation of LATS1 and LATS2 in 14 cases (17%) and 25 cases (30%), respectively. Overall, 62 cases (76%) had at least 1 alteration in the NF2, LATS1, and/or LATS2 genes. Immunohistochemistry revealed nuclear YAP expression in 18 of 42 cases of schwannoma (43%) and reduced cytoplasmic phosphorylated YAP expression in 15 of 49 cases of schwannoma (31%), all of which had at least 1 alteration in the NF2, LATS1, and/or LATS2 genes. These results suggest that an abnormal Hippo signaling pathway is involved in the pathogenesis of most sporadic schwannomas.

Glioblastomas with a proneural expression signature are characterized by frequent IDH1 mutations (i.e. genetic hallmarks of secondary glioblastomas) and PDGFRA (platelet-derived growth factor receptor-α) amplification. Mutations in IDH1/2 are frequent and early genetic events in diffuse astrocytomas (World Health Organization grade II), precursor to secondary glioblastomas, but little is known about the role and timing of PDGFRA amplification in these tumors. We assessed PDGFRA gain in 342 low-grade diffuse gliomas by quantitative polymerase chain reaction. Gain in PDGFRA was detected in 27 (16.3%) of 166 diffuse astrocytomas, significantly more frequent than in oligodendrogliomas (3 [2.6%] of 115, p < 0.0001). Analyses using previously published data from our laboratory showed an inverse correlation between PDGFRA gain and IDH1/2 mutations (p = 0.018) or 1p/19q loss (p < 0.0001). The vast majority of diffuse astrocytomas showed IDH1/2 mutations and/or PDGFRA gain (154 [93%] of 166). Mean survival of diffuse astrocytoma patients with PDGFRA gain was 8.8 ± 1.6 years, similar to that with IDH1/2 mutations (7.8 ± 0.5 years) or TP53 mutations (7.6 ± 0.6 years) but significantly longer than those with MET gain (4.4 ± 0.7 years). Dual-color fluorescence in situ hybridization in 6 diffuse astrocytomas with PDGFRA/MET co-gain identified by quantitative polymerase chain reaction revealed that PDGFRA and MET were typically amplified in different tumor cell populations. Tumor cells with coamplification were also focally observed, suggesting intratumoral heterogeneity, even in diffuse astrocytomas.

Primary glioblastomas develop with a short clinical history, without evidence for less malignant precursor lesions, while secondary glioblastomas slowly develop via progression from diffuse astrocytoma (WHO grade II) or anaplastic astrocytoma (WHO grade III). The time until progression and the clinical outcome of diffuse astrocytomas vary significantly. We have shown that IDH1 mutations reliably distinguish between primary glioblastomas (without IDH1 mutations) and secondary glioblastomas (with IDH1 mutations). The most frequent genetic alteration shared by primary and secondary glioblastomas is loss of heterozygosity at 10q (up to 60% of cases). Here, we first assessed The Cancer Genome Atlas data to identify gene loss at 10q in glio-blastomas with or without IDH1 mutations. Using log-ratio thresholds of −1.0, 10 genes were identified; with the log-ratio thresholds of −2.0, only the DMBT1 (deleted in malignant brain tumor 1) gene at 10q26.13 remained as a deleted gene in glioblastomas with or without IDH1 mutations (12.5% vs 8.0%). We then analyzed a total of 404 gliomas by differential polymerase chain reaction and found a DMBT1 homozygous deletion at a similar frequency in primary and secondary glioblastomas (19.6% vs 20.8%). A fraction (11.3%) of diffuse astro-cytomas showed a DMBT1 homozygous deletion that was significantly associated with a shorter overall survival (52.8 vs 84.0 months; p = 0.003). These results indicate that a DMBT1 homozygous deletion is present in a fraction of diffuse astrocytomas and that it is associated with an unfavorable clinical outcome.