Ganglioglioma (GG) with anaplasia (anaplastic ganglioglioma) is a rare and controversial diagnosis. When present, anaplasia involves the glial component of the tumor, either at presentation or at recurrence. To date, most published cases lack molecular characterization. We describe the histologic and molecular features of 3 patients presenting with BRAF p. V600E-mutant GG (CNS WHO grade 1) with high-grade glial transformation at recurrence. The tumors occurred in pediatric patients (age 9-16 years) with time to recurrence from 20 months to 7 years. At presentation, each tumor was low-grade, with a BRAFV600E-positive ganglion cell component and a glial component resembling pleomorphic xanthoastrocytoma (PXA) or fibrillary astrocytoma. At recurrence, tumors resembled anaplastic PXA or high-grade astrocytomas without neuronal differentiation. CDKN2A homozygous deletion (HD) was absent in all primary tumors. At recurrence, 2 cases acquired CDKN2A HD; the third case showed loss of p16 and MTAP immunoexpression, but no CDKN2A/B HD or mutation was identified. By DNA methylation profiling, all primary and recurrent tumors either grouped or definitely matched to different methylation classes. Our findings indicate that malignant progression of the glial component can occur in GG and suggest that CDKN2A/B inactivation plays a significant role in this process.

We report a case of pediatric glioma with uncommon imaging, morphological, and genetic features. A one-year-old boy incidentally presented with a tumor in the fourth ventricle. The tumor was completely resected surgically and investigated pathologically. The mostly circumscribed tumor had piloid features but primitive and anaplastic histology, such as increasing cellularity and mitosis. The Ki-67 staining index was 25% at the hotspot. KIAA1549::BRAF fusion and KIAA1549 partial deletions were detected by direct PCR, supported by Sanger sequencing. To the best of our knowledge, this is the first report of a glioma with both deletion of KIAA1549 p.P1771_P1899 and fusion of KIAA1549::BRAF. The tumor could not be classified using DNA methylome analysis. The present tumor fell into the category of pilocytic astrocytoma with histological features of anaplasia (aPA). Further studies are needed to establish pediatric aPA.

We report a case of subependymal giant cell astrocytoma (SEGA) with anaplastic histological features in a 3-year-old girl. She had no clinical manifestations of tuberous sclerosis complex (TSC) and no relevant family history. A few cases have been reported in which patients with SEGA had no other clinical manifestations of TSC (solitary SEGA). Genetic analysis using a blood sample from the patient showed no germline alterations in TSC1 or TSC2 genes, while the tumor tissue exhibited loss of heterozygosity (LOH) in TSC2. SEGAs are benign, slowly growing tumors that rarely have significant mitotic activity. However, histopathological examination in the present case revealed high mitotic activity and necrosis besides the typical large plump cells arranged in sheets. This may be the first genetically proven case of a solitary SEGA with histopathological anaplastic features. In this report, we reviewed solitary SEGAs and histopathological malignancy in SEGA.

Anaplasia may be identified in a subset of tumors with a presumed pilocytic astrocytoma (PA) component or piloid features, which may be associated with aggressive behavior, but the biologic basis of this change remains unclear. Fifty-seven resections from 36 patients (23 M, 13 F, mean age 32 years, range 3-75) were included. A clinical diagnosis of NF1 was present in 8 (22%). Alternative lengthening of telomeres (ALT) was assessed by telomere-specific FISH and/or CISH. A combination of immunohistochemistry, DNA sequencing and FISH were used to study BRAF, ATRX, CDKN2A/p16, mutant IDH1 p.R132H and H3-K27M proteins. ALT was present in 25 (69%) cases and ATRX loss in 20 (57%), mostly in the expected association of ALT+/ATRX- (20/24, 83%) or ALT-/ATRX+ (11/11, 100%). BRAF duplication was present in 8 (of 26) (31%). H3-K27M was present in 5 of 32 (16%) cases, all with concurrent ATRX loss and ALT. ALT was also present in 9 (of 11) cases in the benign PA precursor, 7 of which also had ATRX loss in both the precursor and the anaplastic tumor. In a single pediatric case, ALT and ATRX loss developed in the anaplastic component only, and in another adult case, ALT was present in the PA-A component only, but ATRX was not tested. Features associated with worse prognosis included subtotal resection, adult vs. pediatric, presence of a PA precursor preceding a diagnosis of anaplasia, necrosis, presence of ALT and ATRX expression loss. ALT and ATRX loss, as well as alterations involving the MAPK pathway, are frequent in PA with anaplasia at the time of development of anaplasia or in their precursors. Additionally, a small subset of PA with anaplasia have H3-K27M mutations. These findings further support the concept that PA with anaplasia is a neoplasm with heterogeneous genetic features and alterations typical of both PA and diffuse gliomas.

The revised World Health Organization classification of central nervous system tumors, published in 2016, has recognized the H3 K27M mutation as a critical genetic signature defining a new group of infiltrative astrocytomas designated as diffuse midline glioma, H3 K27M mutant. Although most H3 K27M mutations arise in the setting of diffusely infiltrative tumors, there are rare reports of compact tumors with low-grade histologic features harboring this mutation. The prevalence and clinical significance of this mutation in pilocytic astrocytomas remain unclear. We report 2 young adult patients with H3 K27M-mutated thalamic pilocytic astrocytomas who presented to medical attention with symptomatic hydrocephalus requiring urgent intervention. We present our experience with this unusual tumor and recommend a treatment paradigm of maximal safe surgical resection followed by chemotherapy and radiation. Stereotactic biopsies may undergrade some adult thalamic pilocytic astrocytomas. Therefore, we recommend that all these tumors be evaluated for the H3 K27M mutation. Further, we think H3 K27M-mutant thalamic pilocytic astrocytomas require aggressive multimodality treatment and these treatments should be guided by the molecular findings, as opposed to the histologic ones.