Subtelomeric analysis of pediatric astrocytoma: subchromosomal instability is a distinctive feature of pleomorphic xanthoastrocytoma

Pleomorphic Xanthoastrocytoma; Clinicopathological spectrum of An Intriguing neoplasm

Background & Objective:

Pleomorphic xanthoastrocytoma (PXA) is a rare primary WHO Grade II astrocytic tumor comprising of < 1% of all astrocytomas. It is generally benign and slow growing however disease progression and malignant transformation with anaplastic features have been infrequently reported. Our objective was to assess clinicopathological characteristics of this rare tumor at our center.

Methods:

A retrospective study was conducted at Aga Khan University Hospital from January 1992 till January 2016. Data was entered on a proforma including patient demographics, clinical features, tumor location, histological features and follow-up, where available.

Results:

Forty Seven cases of PXA were retrieved during the study period. The mean age was 23.8 years (SD=15.1) and median age was 19 years. The most frequent symptom was head ache (n=31). Male were more frequently affected (n=26). The commonest location was temporal lobe. On microscopic examination, tumors were pleomorphic without mitoses or necrosis, however two cases showed increased mitotic activity, and one case revealed associated gliosarcoma. Follow-up of only 29 cases was available for a period ranging between 2 and 184 months (85 months +/- 56 months). Outcome was good in 27 patients with the last follow up showing no radiographic or clinical evidence of tumor recurrence.

Conclusions:

PXA is an infrequent tumor in our population also, with less than 50 cases identified in two decades study period. Due to its rarity and its bizarre histomorphology, it should be diagnosed correctly, as it has got better prognosis than other astrocytic tumors.

Rare Primary Central Nervous System Tumors Encountered in Pediatrics

As part of the special issue on Pediatric Neuro-Oncology, this article will focus on 4 of the rarer tumors in this spectrum, including atypical teratoid rhabdoid tumors, embryonal tumors with multilayered rosettes, choroid plexus tumors, and pleomorphic xanthoastrocytoma. Incidence and current understanding of the molecular pathogenesis of these tumors are discussed, and avenues of therapy both current and prospective are explored.

Aggressive behavior and anaplasia in pleomorphic xanthoastrocytoma: a plea for a revision of the current WHO classification

Pleomorphic xanthoastrocytoma (PXA) is a rare astrocytic neoplasm that commonly affects children and young adults, and presents with seizures. PXA is typically supratentorial with a predilection to the temporal lobe, and often involves the cortex and the meninges. PXAs have a favorable prognosis with a 10-year survival probability of >70%, and are WHO grade II neoplasms. Recent observations and studies demonstrate that PXAs are clinically, histologically and genetically distinct. Some PXAs recur and exhibit aggressive clinical behavior. In such cases, certain histological and clinical factors could account for the aggressive behavior. However, the histological features that predict adverse outcome are poorly defined. In the current WHO classification of CNS tumors, there is no option for a high-grade PXA, even if the tumor had numerous recurrences and poor outcome. In this review, we focus on aggressive clinical behavior and anaplasia in PXA, and discuss how our current experience suggests modifications in the current WHO classification. We also review recent discoveries on the molecular characteristics of PXA that could help us better understand their biological behavior.

The molecular biology of WHO grade II gliomas

The WHO grading scheme for glial neoplasms assigns Grade II to 5 distinct tumors of astrocytic or oligodendroglial lineage: diffuse astrocytoma, oligodendroglioma, oligoastrocytoma, pleomorphic xanthoastrocytoma, and pilomyxoid astrocytoma. Although commonly referred to collectively as among the "low-grade gliomas," these 5 tumors represent molecularly and clinically unique entities. Each is the subject of active basic research aimed at developing a more complete understanding of its molecular biology, and the pace of such research continues to accelerate. Additionally, because managing and predicting the course of these tumors has historically proven challenging, translational research regarding Grade II gliomas continues in the hopes of identifying novel molecular features that can better inform diagnostic, prognostic, and therapeutic strategies. Unfortunately, the basic and translational literature regarding the molecular biology of WHO Grade II gliomas remains nebulous. The authors' goal for this review was to present a comprehensive discussion of current knowledge regarding the molecular characteristics of these 5 WHO Grade II tumors on the chromosomal, genomic, and epigenomic levels. Additionally, they discuss the emerging evidence suggesting molecular differences between adult and pediatric Grade II gliomas. Finally, they present an overview of current strategies for using molecular data to classify low-grade gliomas into clinically relevant categories based on tumor biology.

Genetic changes observed in a case of adult pilocytic astrocytoma revealed by array CGH analysis

BACKGROUND

A palette of copy number changes in a case of adult pilocytic astrocytoma analyzed by Array Comparative Genomic Hybridization (aCGH) is presented. Pilocytic astrocytomas are specific gliomas that are benign and biologically distinct and the molecular mechanisms responsible for their development remain unexplained. The aCGH was performed using SurePrint G3 Human CGH microarrays 4 × 180 K (Agilent Technologies). To ascertain whether some of the aberrations were of constitutive nature, we also analyzed the blood sample from the same patient.

RESULTS

The result of aCGH analysis demonstrated differences in the tumor tissue when compared to normal control on the array and also to autologous DNA from patient's blood. The total number of aberrations found in our case was 41 including 37 deletions and 4 amplifications. Whole chromosomal gains and losses were not observed. Collectively, our results showed three deletions and one amplification at 1p, two deletions at 2q, two deletions at 4q, two deletion at 5q, two deletions at 7p and two deletions at 7q; there were also three deletions at 8q, one deletion at 9p, one deletion at 10p, three deletions and one amplification at 10q. Chromosome 11 showed two deletions at 11p, while there was one deletion at 12p and one at 12q. Four deletions at 14q; two deletions at 15q, one amplification at 17q and one deletion at 17q; one deletion at 18p, two deletions at 22q and finally one deletion at Xp and one deletion and one amplification at Xq. Among the signaling pathways, olfactory transduction, Fc gamma R-mediated phagocytosis and p53 signaling pathway showed significant enrichment ascertained by gene ontology (GO) analysis using the DAVID software.

CONCLUSIONS

Our aCGH analysis is bringing subtle genomic alterations thus broadening genetic spectrum of adult pilocytic astrocytoma in order to offer new molecular biomarkers that will help in diagnostics and therapeutic decision-making.

Pleomorphic Xanthoastrocytoma: Natural History and Long-Term Follow-Up

Prognostic significance of histological anaplasia and BRAF V600E mutation were retrospectively evaluated in 74 patients with pleomorphic xanthoastrocytoma (PXA). Median age at diagnosis was 21.5 years (31 pediatric, 43 adult) and median follow-up 7.6 years. Anaplasia (PXA-AF), defined as mitotic index ≥ 5/10 HPF and/or presence of necrosis, was present in 33 cases. BRAF V600E mutation was detected in 39 (of 60) cases by immunohistochemical and/or molecular analysis, all negative for IDH1 (R132H). Mitotic index ≥ 5/10 HPF and necrosis were associated with decreased overall survival (OS; P = 0.0005 and P = 0.0002, respectively). In all cases except two, necrosis was associated with mitotic index ≥ 5/10 HPF. Patients with BRAF V600E mutant tumors had significantly longer OS compared with those without BRAF V600E mutation (P = 0.02). PXA-AF patients, regardless of age, had significantly shorter OS compared with those without (P = 0.0003). Recurrence-free survival was significantly shorter for adult PXA-AF patients (P = 0.047) only. Patients who either recurred or died ≤ 3 years from diagnosis were more likely to have had either PXA-AF at first diagnosis (P = 0.008) or undergone a non-gross total resection procedure (P = 0.004) as compared with patients who did not. This study provides further evidence that PXA-AF behaves more aggressively than PXA and may qualify for WHO grade III "anaplastic" designation.

DNA methylation alterations in grade II- and anaplastic pleomorphic xanthoastrocytoma

Background

Pleomorphic xanthoastrocytoma (PXA) is a rare WHO grade II tumor accounting for less than 1% of all astrocytomas. Malignant transformation into PXA with anaplastic features, is unusual and correlates with poorer outcome of the patients.

Methods

Using a DNA methylation custom array, we have quantified the DNA methylation level on the promoter sequence of 807 cancer-related genes of WHO grade II (n = 11) and III PXA (n = 2) and compared to normal brain tissue (n = 10) and glioblastoma (n = 87) samples. DNA methylation levels were further confirmed on independent samples by pyrosequencing of the promoter sequences.

Results

Increasing DNA promoter hypermethylation events were observed in anaplastic PXA as compared with grade II samples. We further validated differential hypermethylation of CD81, HCK, HOXA5, ASCL2 and TES on anaplastic PXA and grade II tumors. Moreover, these epigenetic alterations overlap those described in glioblastoma patients, suggesting common mechanisms of tumorigenesis.

Conclusions

Even taking into consideration the small size of our patient populations, our data strongly suggest that epigenome-wide profiling of PXA is a valuable tool to identify methylated genes, which may play a role in the malignant progression of PXA. These methylation alterations may provide useful biomarkers for decision-making in those patients with low-grade PXA displaying a high risk of malignant transformation.

The molecular biology of WHO grade I astrocytomas

World Health Organization (WHO) grade I astrocytomas include pilocytic astrocytoma (PA) and subependymal giant cell astrocytoma (SEGA). As technologies in pharmacologic neo-adjuvant therapy continue to progress and as molecular characteristics are progressively recognized as potential markers of both clinically significant tumor subtypes and response to therapy, interest in the biology of these tumors has surged. An updated review of the current knowledge of the molecular biology of these tumors is needed. We conducted a Medline search to identify published literature discussing the molecular biology of grade I astrocytomas. We then summarized this literature and discuss it in a logical framework through which the complex biology of these tumors can be clearly understood. A comprehensive review of the molecular biology of WHO grade I astrocytomas is presented. The past several years have seen rapid progress in the level of understanding of PA in particular, but the molecular literature regarding both PA and SEGA remains nebulous, ambiguous, and occasionally contradictory. In this review we provide a comprehensive discussion of the current understanding of the chromosomal, genomic, and epigenomic features of both PA and SEGA and provide a logical framework in which these data can be more readily understood.