Comparative molecular analysis of primary and recurrent oligodendroglioma that acquired imbalanced 1p/19q codeletion and TP53 mutation: a case report

Recurrent oligodendroglioma with changed 1p/19q status

We report a case of oligodendroglioma that had consistent histopathological features as well as a distinct change in 1p/19q status in the second recurrence, after temozolomide chemotherapy and radiotherapy. The first tumor recurrence had oligodendroglial morphology, IDH1 R132H and TERT promoter mutations, and 1p/19q codeletion detected by fluorescent in situ hybridization (FISH). Copy number analysis, assessed by next‐generation sequencing, confirmed 1p/19q codeletion, and disclosed loss of heterozygosity (LOH) of chromosomes 4 and 9 and chromosome 11 gain. The second recurrence featured not only oligodendroglial morphology but also the appearance of admixed multinucleated giant cells or neoplastic cells having oval nuclei and mitoses and showing microvascular proliferation; it maintained IDH1 R132H and TERT promoter mutations, acquired TP53 mutation, and showed 19q LOH, but disomic 1p, detected by FISH. Copy number analysis depicted LOH of chromosomes 3p, 13, and 19q, 1p partial deletion (1p chr1p34.2‐p11), and gain of chromosomes 2p25.3‐p24.1, 8q12.2‐q24.3, and 11q13.3‐q25. B‐allele frequency analysis of polymorphic sites disclosed copy‐neutral LOH at 1p36.33‐p34.2, supporting the initial deletion of 1p, followed by reduplication of 1p36.33‐p34.2 alone. These findings suggest that the two tumor recurrences might have originated from an initial neoplastic clone, featuring 1p/19q codeletion and IDH1 and TERT promoter mutations, and have independently acquired other copy number alterations. The reduplication of chromosome 1p might be the result of temozolomide treatment, and gave rise to false negative 1p deletion detected by FISH. The possibility of 1p copy‐neutral LOH should be considered in recurrent oligodendrogliomas with altered 1p/19q status detected by FISH.

Oligosarcomas, IDH-mutant are distinct and aggressive

Oligodendrogliomas are defined at the molecular level by the presence of an IDH mutation and codeletion of chromosomal arms 1p and 19q. In the past, case reports and small studies described gliomas with sarcomatous features arising from oligodendrogliomas, so called oligosarcomas. Here, we report a series of 24 IDH-mutant oligosarcomas from 23 patients forming a distinct methylation class. The tumors were recurrences from prior oligodendrogliomas or developed de novo. Precursor tumors of 12 oligosarcomas were histologically and molecularly indistinguishable from conventional oligodendrogliomas. Oligosarcoma tumor cells were embedded in a dense network of reticulin fibers, frequently showing p53 accumulation, positivity for SMA and CALD1, loss of OLIG2 and gain of H3K27 trimethylation (H3K27me3) as compared to primary lesions. In 5 oligosarcomas no 1p/19q codeletion was detectable, although it was present in the primary lesions. Copy number neutral LOH was determined as underlying mechanism. Oligosarcomas harbored an increased chromosomal copy number variation load with frequent CDKN2A/B deletions. Proteomic profiling demonstrated oligosarcomas to be highly distinct from conventional CNS WHO grade 3 oligodendrogliomas with consistent evidence for a smooth muscle differentiation. Expression of several tumor suppressors was reduced with NF1 being lost frequently. In contrast, oncogenic YAP1 was aberrantly overexpressed in oligosarcomas. Panel sequencing revealed mutations in NF1 and TP53 along with IDH1/2 and TERT promoter mutations. Survival of patients was significantly poorer for oligosarcomas as first recurrence than for grade 3 oligodendrogliomas as first recurrence. These results establish oligosarcomas as a distinct group of IDH-mutant gliomas differing from conventional oligodendrogliomas on the histologic, epigenetic, proteomic, molecular and clinical level. The diagnosis can be based on the combined presence of (a) sarcomatous histology, (b) IDH-mutation and (c) TERT promoter mutation and/or 1p/19q codeletion, or, in unresolved cases, on its characteristic DNA methylation profile.