Comprehensive analysis of MYB/MYBL1-altered pediatric-type diffuse low-grade glioma.

BACKGROUND: Pediatric-type diffuse low-grade gliomas (pLGG) harboring recurrent genetic alterations involving MYB or MYBL1 are closely related tumors. Detailed treatment and outcome data of large cohorts are still limited. This study aimed to comprehensively evaluate pLGG with these alterations to define optimal therapeutic strategies. METHODS: We retrospectively reviewed details of pLGG with MYB or MYBL1 alterations from patients treated or referred for pathologic review at St. Jude Children's Research Hospital. Tumor specimens were centrally reviewed, and clinical data were collated. RESULTS: Thirty-three patients (18 male; median age, 5 years) were identified. Two tumors had MYBL1 alterations; 31 had MYB alterations, MYB::QKI fusion being the most common (n = 10, 30%). Most tumors were in the cerebral hemispheres (n = 22, 67%). Two patients (6%) had metastasis at diagnosis. The median follow-up was 6.1 years. The 5-year event-free survival (EFS) rate was 81.3% ±â€…8.3%; the 5-year overall survival (OS) rate was 96.4% ±â€…4.1%. Patients receiving a near-total or gross-total resection had a 5-year EFS of 100%; those receiving a biopsy or subtotal resection had a 5-year EFS rate of 56.6% ±â€…15.2% (P < .01). No difference in EFS was observed based on location, histology, or molecular alterations. However, the tumors that progressed or metastasized may have distinct methylation profiles with evidence of activation of the MAPK and PI3K/AKT/mTOR pathways. CONCLUSIONS: pLGG with MYB/MYBL1 alterations have good outcomes. Our findings suggest that surgical resectability is a crucial determinant of EFS. Further characterization is required to identify optimal treatment strategies for progressive tumors.

Multiplatform molecular analyses refine classification of gliomas arising in patients with neurofibromatosis type 1.

Gliomas arising in the setting of neurofibromatosis type 1 (NF1) are heterogeneous, occurring from childhood through adulthood, can be histologically low-grade or high-grade, and follow an indolent or aggressive clinical course. Comprehensive profiling of genetic alterations beyond NF1 inactivation and epigenetic classification of these tumors remain limited. Through next-generation sequencing, copy number analysis, and DNA methylation profiling of gliomas from 47 NF1 patients, we identified 2 molecular subgroups of NF1-associated gliomas. The first harbored biallelic NF1 inactivation only, occurred primarily during childhood, followed a more indolent clinical course, and had a unique epigenetic signature for which we propose the terminology "pilocytic astrocytoma, arising in the setting of NF1". The second subgroup harbored additional oncogenic alterations including CDKN2A homozygous deletion and ATRX mutation, occurred primarily during adulthood, followed a more aggressive clinical course, and was epigenetically diverse, with most tumors aligning with either high-grade astrocytoma with piloid features or various subclasses of IDH-wildtype glioblastoma. Several patients were treated with small molecule MEK inhibitors that resulted in stable disease or tumor regression when used as a single agent, but only in the context of those tumors with NF1 inactivation lacking additional oncogenic alterations. Together, these findings highlight recurrently altered pathways in NF1-associated gliomas and help inform targeted therapeutic strategies for this patient population.

Targeted Next-Generation Sequencing Reveals Divergent Clonal Evolution in Components of Composite Pleomorphic Xanthoastrocytoma-Ganglioglioma.

Composite pleomorphic xanthoastrocytoma-ganglioglioma (PXA-GG) is an extremely rare central nervous system neoplasm with 2 distinct but intermingled components. Whether this tumor represents a "collision tumor" of separate neoplasms or a monoclonal neoplasm with divergent evolution is poorly understood. Clinicopathologic studies and capture-based next generation sequencing were performed on extracted DNA from all available PXA-GG at 2 medical centers. Five PXA-GG were diagnosed in 1 male and 4 female patients ranging from 13 to 25 years in age. Four arose within the cerebral hemispheres; 1 presented in the cerebellar vermis. DNA was sufficient for analysis in 4 PXA components and 3 GG components. Four paired PXA and GG components harbored BRAF p.V600E hotspot mutations. The 4 sequenced PXA components demonstrated CDKN2A homozygous deletion by sequencing with loss of p16 (protein product of CDKN2A) expression by immunohistochemistry, which was intact in all assessed GG components. The PXA components also demonstrated more frequent copy number alterations relative to paired GG components. In one PXA-GG, shared chromosomal copy number alterations were identified in both components. Our findings support divergent evolution of the PXA and GG components from a common BRAF p.V600E-mutant precursor lesion, with additional acquisition of CDKN2A homozygous deletion in the PXA component as is typically seen in conventional PXA.

The immunohistochemical, DNA methylation, and chromosomal copy number profile of cauda equina paraganglioma is distinct from extra-spinal paraganglioma.

Paragangliomas are neuroendocrine tumors of the autonomic nervous system that are variably clinically functional and have a potential for metastasis. Up to 40% occur in the setting of a hereditary syndrome, most commonly due to germline mutations in succinate dehydrogenase (SDHx) genes. Immunohistochemically, paragangliomas are characteristically GATA3-positive and cytokeratin-negative, with loss of SDHB expression in most hereditary cases. In contrast, the rare paragangliomas arising in the cauda equina (CEP) or filum terminale region have been shown to be hormonally silent, clinically indolent, and have variable keratin expression, suggesting these tumors may represent a separate pathologic entity. We retrospectively evaluated 17 CEPs from 11 male and 6 female patients with a median age of 38 years (range 21-82), none with a family history of neuroendocrine neoplasia. Six of the 17 tumors demonstrated prominent gangliocytic or ganglioneuromatous differentiation. By immunohistochemistry, none of the CEPs showed GATA3 positivity or loss of SDHB staining; all 17 CEPs were cytokeratin positive. Genome-wide DNA methylation profiling was performed on 12 of the tumors and compared with publicly available genome-wide DNA methylation data. Clustering analysis showed that CEPs form a distinct epigenetic group, separate from paragangliomas of extraspinal sites, pheochromocytomas, and other neuroendocrine neoplasms. Copy number analysis revealed diploid genomes in the vast majority of CEPs, whereas extraspinal paragangliomas were mostly aneuploid with recurrent trisomy 1q and monosomies of 1p, 3, and 11, none of which were present in the cohort of CEP. Together, these findings indicate that CEPs likely represent a distinct entity. Future genomic studies are needed to further elucidate the molecular pathogenesis of these tumors.