Role of a Promoter Mutation in TERT in Malignant Transformation of Pleomorphic Xanthoastrocytoma

Clinical, Morphological, and Molecular Study on Grade 2 and 3 Pleomorphic Xanthoastrocytoma

PURPOSE

Pleomorphic xanthoastrocytoma (PXA) is an uncommon astrocytoma that tends to occur in children and young adults and has a relatively favorable prognosis. The 2021 WHO classification of tumors of the central nervous system (CNS WHO), 5th edition, rates PXAs as grade 2 and grade 3. The histological grading was based on mitotic activity (≥2.5 mitoses/mm²). This study specifically evaluates the clinical, morphological, and, especially, the molecular characteristics of grade 2 and 3 PXAs.

METHODS

Between 2003 and 2021, we characterized 53 tumors with histologically defined grade 2 PXA (n = 36, 68%) and grade 3 PXA (n = 17, 32%).

RESULTS

Compared with grade 2 PXA, grade 3 PXA has a deeper location and no superiority in the temporal lobe and is more likely to be accompanied by peritumoral edema. In histomorphology, epithelioid cells and necrosis were more likely to occur in grade 3 PXA. Molecular analysis found that the TERT promoter mutation was more prevalent in grade 3 PXA than in grade 2 PXA (35% vs. 3%; p = 0.0005) and all mutation sites were C228T. The cases without BRAF V600E mutation or with necrosis in grade 3 PXA had a poor prognosis (p = 0.01).

CONCLUSION

These data define PXA as a heterogeneous astrocytoma. Grade 2 and grade 3 PXAs have different clinical and histological characteristics as well as distinct molecular profiles. TERT promoter mutations may be a significant genetic event associated with anaplastic progression. Necrosis and BRAF V600E mutation play an important role in the prognosis of grade 3 PXA.

Anaplastic ganglioglioma - a diagnosis comprising several distinct tumour types

Anaplastic ganglioglioma is a rare tumour and diagnosis has been based on histological criteria. The 5^th edition of the World Health Organization Classification of Tumours of the Central Nervous System (CNS WHO) does not list anaplastic ganglioglioma as a distinct diagnosis due to lack of molecular data in previous publications AIM: We retrospectively compiled a cohort of 54 histologically diagnosed anaplastic gangliogliomas to explore whether the molecular profiles of these tumours represent a separate type or resolve into other entities METHODS: Samples were subjected to histological review, DNA methylation profiling and next generation sequencing. Morphologic and molecular data were summarised to an integrated diagnosis RESULTS: The majority of histologically diagnosed anaplastic gangliogliomas resolved into CNS WHO diagnoses of glial tumours, most commonly pleomorphic xanthoastrocytoma (16/54), glioblastoma, IDH wildtype and diffuse paediatric-type high-grade glioma, H3 wildtype and IDH wildtype (11 and 2/54) followed by low-grade glial or glioneuronal tumours including pilocytic astrocytoma, dysembryoplastic neuroepithelial tumour and diffuse leptomeningeal glioneuronal tumour (5/54), IDH mutant astrocytoma (4/54) and others (6/54). A subset of tumours (10/54) was not assignable to a CNS WHO diagnosis and common molecular profiles pointing to a separate entity were not evident CONCLUSION: In summary, we show that tumours histologically diagnosed as anaplastic ganglioglioma comprise a wide spectrum of CNS WHO tumour types with different prognostic and therapeutic implications. We therefore suggest assigning this designation with caution and recommend comprehensive molecular workup.

Molecular landscape of pediatric type IDH wildtype, H3 wildtype hemispheric glioblastomas

The WHO (2021) Classification classified a group of pediatric-type high-grade gliomas as IDH wildtype, H3 wildtype but as of currently, they are characterized only by negative molecular features of IDH and H3. We recruited 35 cases of pediatric IDH wildtype and H3 wildtype hemispheric glioblastomas. We evaluated them with genome-wide methylation profiling, targeted sequencing, RNAseq, TERT promoter sequencing, and FISH. The median survival of the cohort was 27.6 months. With Capper et al.'s³⁶ methylation groups as a map, the cases were found to be epigenetically heterogeneous and were clustered in proximity or overlay of methylation groups PXA-like (n = 8), LGG-like (n = 10), GBM_MYCN (n = 9), GBM_midline (n = 5), and GBM_RTKIII (n = 3). Histology of the tumors in these groups was not different from regular glioblastomas. Methylation groups were not associated with OS. We were unable to identify groups specifically characterized by EGFR or PDGFRA amplification as proposed by other authors. EGFR, PDGFRA, and MYCN amplifications were not correlated with OS. 4/9 cases of the GBM_MYCN cluster did not show MYCN amplification; the group was also enriched for EGFR amplification (4/9 cases) and the two biomarkers overlapped in two cases. Overall, PDGFRA amplification was found in only four cases and they were not restricted to any groups. Cases in proximity to GBM_midline were all hemispheric and showed loss of H3K27me3 staining. Fusion genes ALK/NTRK/ROS1/MET characteristic of infantile glioblastomas were not identified in 17 cases successfully sequenced. BRAF V600E was only found in the PXA group but CDKN2A deletion could be found in other methylation groups. PXA-like cases did not show PXA histological features similar to findings by other authors. No case showed TERT promoter mutation. Mutations of mismatch repair (MMR) genes were poor prognosticators in single (p ≤ 0.001) but not in multivariate analyses (p = 0.229). MGMT had no survival significance in this cohort. Of the other common biomarkers, only TP53 and ATRX mutations were significant poor prognosticators and only TP53 mutation was significant after multivariate analyses (p = 0.024). We conclude that IDH wildtype, H3 wildtype pediatric hemispheric glioblastomas are molecularly heterogeneous and in routine practice, TP53, ATRX, and MMR status could profitably be screened for risk stratification in laboratories without ready access to methylation profiling.

The evolution of pleomorphic xanthoastrocytoma: from genesis to molecular alterations and mimics

Pleomorphic xanthoastrocytomas (PXAs) are rare tumors accounting for less than 1% of astrocytomas. They commonly occur in young patients and have relatively favorable prognosis. However, they are well known to have heterogenous morphology and biological behavior with the potential to recur and disseminate throughout the central nervous system, especially their anaplastic counterparts. Recent advances in the molecular characterization have discovered BRAFp.V600E mutations in conjunction with CDKN2A/B deletions and TERTp mutations to be the most frequent alterations in PXAs. These tumors can present a diagnostic challenge as they share overlapping histopathological, genomic as well as methylation profile with various other tumor types, particularly epithelioid glioblastomas (eGBs). This review provides the spectrum of evolution of PXAs from their genesis to recent molecular insights and attempts to review pathogenesis and relationship to other tumors that they mimic especially eGB. It is postulated based on evidence from literature that PXA and eGB are possibly related and not distinct entities, being two ends of a continuous spectrum of malignant progression (grade 2-grade 4) with anaplastic PXA (grade 3) lying in between. Future WHO classifications will have to possibly redefine these tumors using more confirmatory data from larger studies.

Molecular landscape of IDH-wildtype, H3-wildtype glioblastomas of adolescents and young adults (AYA)

OBJECTIVE

We aimed to characterise glioblastomas of adolescents and young adults (AYA) that were IDH wildtype (wt) and H3 wildtype (wt).

MATERIALS AND METHODS

Fifty such patients (aged 16-32) were studied by methylation profiling, targeted sequencing and targeted RNA-seq.

RESULTS

Tumours predominantly clustered into three methylation classes according to the terminology of Capper et al. (2018): (anaplastic) PXA (21 cases), GBM_midline (15 cases) and glioblastoma RTK/mesenchymal (7 cases). Two cases clustered with ANA_PA, 4 cases with LGG classes and 1 with GBM_MYCN. Only fifteen cases reached a calibrated score >0.84 when the cases were uploaded to DKFZ Classifier. GBM_midline-clustered tumours had a poorer overall survival (OS) compared to the PXA-clustered tumours (p=0.030). LGG-clustered cases had a significantly better survival than GBM_midline-clustered tumours and glioblastoma RTK/mesenchymal-clustered tumours. Only 13/21 (62%) of PXA-clustered cases were BRAF V600E mutated. Most GBM_midline-clustered cases were not located in the midline. GBM_midline-clustered cases were characterized by PDGFRA amplification/mutation (73.3%), mutations of mismatch repair genes (40.0%), and all showed H3K27me3 and EZH1P loss, and an unmethylated MGMT promoter. Across the whole cohort, MGMT promoter methylation and wildtype TERT promoter were favourable prognosticators. Mismatch repair gene mutations were poor prognosticators and together with methylation class and MGMT methylation, maintained their significance in multi-variate analyses. BRAF mutation was a good prognosticator in the PXA-clustered tumours.

CONCLUSION

Methylation profiling is a useful tool in the diagnosis and prognostication of AYA glioblastomas and the methylation classes have distinct molecular characteristics. The usual molecular diagnostic criteria for adult IDHwt glioblastoma should be applied with caution within the AYA age group.

Pleomorphic xanthoastrocytoma is a heterogeneous entity with pTERT mutations prognosticating shorter survival

Pleomorphic xanthoastrocytoma (PXA) in its classic manifestation exhibits distinct morphological features and is assigned to CNS WHO grade 2 or grade 3. Distinction from glioblastoma variants and lower grade glial and glioneuronal tumors is a common diagnostic challenge. We compared a morphologically defined set of PXA (histPXA) with an independent set, defined by DNA methylation analysis (mcPXA). HistPXA encompassed 144 tumors all subjected to DNA methylation array analysis. Sixty-two histPXA matched to the methylation class mcPXA. These were combined with the cases that showed the mcPXA signature but had received a histopathological diagnosis other than PXA. This cohort constituted a set of 220 mcPXA. Molecular and clinical parameters were analyzed in these groups. Morphological parameters were analyzed in a subset of tumors with FFPE tissue available. HistPXA revealed considerable heterogeneity in regard to methylation classes, with methylation classes glioblastoma and ganglioglioma being the most frequent mismatches. Similarly, the mcPXA cohort contained tumors of diverse histological diagnoses, with glioblastoma constituting the most frequent mismatch. Subsequent analyses demonstrated the presence of canonical pTERT mutations to be associated with unfavorable prognosis among mcPXA. Based on these data, we consider the tumor type PXA to be histologically more varied than previously assumed. Histological approach to diagnosis will predominantly identify cases with the established archetypical morphology. DNA methylation analysis includes additional tumors in the tumor class PXA that share similar DNA methylation profile but lack the typical morphology of a PXA. DNA methylation analysis also assist in separating other tumor types with morphologic overlap to PXA. Our data suggest the presence of canonical pTERT mutations as a robust indicator for poor prognosis in methylation class PXA.

Cerebral pleomorphic xanthoastrocytoma mimicking inflammatory granuloma: Two case reports

RATIONALE

Pleomorphic xanthoastrocytoma (PXA) is a rare low-grade glial neoplasm of the central nervous system, which is difficult to distinguish from other neoplastic and non-neoplastic entities. Herein, we report 2 cases of PXA that had been misdiagnosed as an inflammatory granuloma.

PATIENT CONCERNS

The first case was a 22-year-old man who originally presented with a generalized seizure 7 years previously. Magnetic resonance imaging (MRI) revealed a lesion in the right parietal lobe, leading to a diagnosis of inflammatory granuloma. The second case was a 43-year-old man who presented with repeated generalized seizures. MRI revealed a nodular lesion in the left temporal lobe. The magnetic resonance spectrum showed elevated Cho and NAA peaks and a decreased Cr peak. An inflammatory granuloma was suspected.

DIAGNOSIS

After surgical treatment, histopathological examination revealed PXA.

INTERVENTIONS

In the first case, after 10 months of anti-inflammatory treatment, the lesion was significantly reduced in size. During the following 7 years, the patient experienced generalized seizures 3 to 4 times annually. To control intractable epilepsy, the lesion was resected. In the second case, conservative treatment provided no benefit, and then the lesion was resected.

OUTCOMES

In the first case, during a follow-up period of 14 months, the patient was seizure-free with no tumor recurrence. In the second case, after a 6 months of follow-up, the patient remained seizure-free with no tumor recurrence.

LESSONS

The preoperative differential diagnosis of PXA is challenging due to the nonspecific symptoms and imaging manifestations. Considering the potential risk of malignant transformation of PXA, early surgery should be highlighted, and gross total resection is associated with a favorable prognosis.

Association between adjuvant radiation therapy and overall survival in Pleomorphic Xanthoastrocytoma

BACKGROUND

Pleomorphic Xanthoastrocytoma (PXA) is a low-grade central nervous system (CNS) tumor with a generally favorable prognosis. However, due to its rarity, optimal adjuvant treatment guidelines have not been established by large scale studies. In this study, we investigated the effect of adjuvant radiation therapy (RT) on overall survival (OS) in adult patients with PXA to help address this unanswered question.

METHODS

The National Cancer Database (NCDB) was used to identify adult patients (age ≥ 18 years old) diagnosed with histologically confirmed grade II PXA (2004-2016). Patient demographics, tumor characteristics, and treatment information were collected. Kaplan-Meier curves were generated to study OS, and factors that affected OS were identified using a multivariate Cox proportional hazards (CPH) model.

RESULTS

A total of 546 patients were identified. The average age of patients at diagnosis was 36.6 years old, and overall median survival was 128.6 months. RT was used to treat 179 (33.3 %) patients. Those who received RT had a shorter median OS (33.3 months) compared to those who did not (>128.6 months, p < 0.001). Our multivariate model demonstrated receiving RT was independently associated with a significantly higher risk of death (hazard ratio [HR] = 4.28, 95 % confidence interval [CI] = 1.77-10.38, p = .0013). Patients ≥65 years of age also demonstrated significantly higher risk of death (HR = 2.20, CI = 1.54-4.16, p = .006) and had a decreased median OS (26.0 months).

CONCLUSION

In adults with PXA, treatment with RT is independently associated with a significantly higher risk of mortality. The routine use of this modality in treating PXA warrants further study.