Small Cell Astrocytoma
This is an interesting case of small cell astrocytoma in a child because of the overall rarity of this specific variant and especially so in pediatric population. In adults, these tumors are thought to behave more like primary glioblastoma, particularly when associated with EGFR amplification and/or PTEN/10q loss even in the absence of microvascular proliferation and/or necrosis (4). The clinical behavior of this particular phenotype is however less clear in children although it appears to be equally aggressive from the illustrated example as well as rare reports in the literature (3). Notably, the presence of the H3F3 K27M mutation, as identified in this pediatric high-grade glioma, is also associated with shorter survival as compared with wild-type tumors (1, 2) . On morphological evaluation, a diagnosis of small cell astrocytoma was favored due to its discrepant findings of relatively uniform nature on low-power, and significant atypia, and brisk mitotic activity on high-power examination. An anaplastic oligodendroglioma was nevertheless a close differential diagnostic consideration, prompting further ancillary studies. Findings of monosomy10/10q and polysomy of chromosome 7 without 1p19q co-deletions were more consistent with a small cell astrocytoma. In summary, this relatively uncommon example of small cell astrocytoma showed molecular features associated with both adult-type (PTEN/10q loss) and pediatric-type (H3K27M mutation) high-grade astrocytoma. Whether or not H3K27M mutation plays any role in rendering astrocytomas with a small cell phenotype a worse prognosis, is rather intriguing and requires further exploration.
Contributed by Katherine E. Schwetye, MD, PhD, Karen Gauvain, MD, David Rodriguez, MD, Catherine Cottrell, PhD, David D. Limbrick, Jr., MD, PhD, Robert E. Schmidt, MD, PhD, Sonika Dahiya, MD