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.

Low-grade (WHO I–II) gliomas and glioneuronal tumors represent the most frequent primary tumors of the central nervous system in children. They often have a good prognosis following total resection, however they can create many neurological complications due to mass effect, and may be difficult to resect depending on anatomic location. MicroRNAs have been identified as molecular regulators of protein expression/translation that can repress multiple mRNAs concurrently through base pairing, and play an important role in cancer, including brain tumors. Using the NanoString digital counting system, we analyzed the expression levels of 800 microRNAs in nine low-grade glial and glioneuronal tumor types (n=45). A set of 61 of these microRNAs were differentially expressed in tumors compared to brain and several showed levels varying by tumor type. The expression differences were more accentuated in subependymal giant cell astrocytoma, compared with other groups, and demonstrated the highest degree of microRNA repression validated by RT-PCR, including miR-129-2-3p, miR-219-5p, miR-338-3p, miR-487b, miR-885-5p, and miR-323a-3p. Conversely, miR-4488 and miR-1246 were overexpressed in dysembryoplastic neuroepithelial tumors compared with brain and other tumors. The cluster 14q32.31 member miR-487b was variably under expressed in pediatric glioma lines compared to human neural stem cells. Overexpression of miR-487b in a pediatric glioma cell line (KNS42) using lentiviral vectors led to a decrease in colony formation in soft agar (30%)(p<0.05), and decreased expression of known predicted targets PROM1 and Nestin (but not WNT5A). miR-487b overexpression had no significant effect on cell growth, proliferation, sensitivity to temozolomide, migration or invasion. In summary, microRNA regulation appears to play a role in the biology of glial and glioneuronal tumor subtypes, a finding that deserves further investigation.