EGFR/CEP7 high polysomy is separate and distinct from EGFR amplification in glioblastoma as determined by fluorescence in situ hybridization

EGFR amplification in gliomas is commonly defined by an EGFR/CEP7 ratio of ≥2. In testing performed at a major reference laboratory, a small subset of patients had ≥5 copies of both EGFR and CEP7 yet were not amplified by the EGFR/CEP7 ratio and were designated high polysomy cases. To determine whether these tumors are more closely related to traditionally defined EGFR-amplified or nonamplified gliomas, a retrospective search identified 22 out of 1143 (1.9%) gliomas with an average of ≥5 copies/cell of EGFR and CEP7 with an EGFR/CEP7 ratio of <2 displaying high polysomy. Of these cases, 4 had insufficient clinicopathologic data to include in additional analysis, 15 were glioblastomas, 2 were IDH-mutant astrocytomas, and 1 was a high-grade glial neoplasm, NOS. Next-generation sequencing available on 3 cases demonstrated one with a TERT promoter mutation, TP53 mutations in all cases, and no EGFR mutations or amplifications, which most closely matched the nonamplified cases. The median overall survival times were 42.86, 66.07, and 41.14 weeks for amplified, highly polysomic, and nonamplified, respectively, and were not significantly different (p =  0.3410). High chromosome 7 polysomic gliomas are rare but our data suggest that they may be biologically similar to nonamplified gliomas.

Clinical, histopathological, and molecular features of IDH-wildtype indolent diffuse glioma: comparison with typical glioblastoma

PURPOSE

IDH-wildtype (IDHwt) diffuse gliomas are treated as glioblastoma, however, some of these may show less aggressive clinical courses. The authors investigated the clinical, histopathological, and molecular characteristics of such IDHwt indolent diffuse gliomas (iDGwt), which have not been well documented in the literature.

METHODS

Adult patients with IDHwt gliomas admitted between 2011 and 2020 were surveyed. In this particular study, the clinical indolence was defined mainly as having a small enhancing lesion and a stable period for more than 1 month before surgery. The current WHO diagnostic criteria were adapted for the diagnoses. Gene mutations and copy number changes in 43 representative glioma-associated genes, MGMT promoter methylation status, and survival data were compared with those of The Cancer Genome Atlas reference cohort.

RESULTS

Nine out of 180 surveyed cases (5.0%) fulfilled the present criteria of the iDGwt. Considering the representative regulatory pathways, 8 (88.9%), 4 (44.4%), and 1 (11.1%) case had genetic alterations in the PI3K/MAPK, TP53, and RB pathways, respectively. The frequency of the RB pathway alteration was significantly lower than that in the reference cohort (281 of 362 cases: 77.6%). Two cases (22.2%) showing EGFR amplification met the diagnostic criteria for glioblastoma, and the frequency was significantly lower than that in the reference cohort (412 of 426 cases: 96.7%). The overall survival (median: 37.5 months) in the present series was significantly longer than that in the reference cohort (n = 426, median: 13.9 months).

CONCLUSIONS

iDGwt lacked the molecular features of glioblastoma except for the PI3K/MAPK pathway alteration.