This article includes discussion of cerebellar astrocytoma, classical juvenile pilocytic astrocytoma, cystic cerebellar astrocytoma, diffuse astrocytoma, juvenile astrocytoma, juvenile pilocytic astrocytoma, and juvenile pilomyxoid astrocytoma. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Cerebellar astrocytomas are the most common benign brain tumor of childhood. Most tumors are pilocytic astrocytomas and are amenable to gross total resections. After such treatment, 95% or more of patients will be cured of disease. For those tumors that cannot be grossly totally resected, including occasional midline pilocytic astrocytomas and other variants of low-grade glioma, attempts at re-resection or, in infrequent situations, radiation therapy or chemotherapy may be indicated. New biological insights suggest that molecular-targeted therapy may be available soon to treat subtotally resected and/or progressive lesions. This clinical article updates the reader in the new concepts of the molecular pathogenesis of the tumor and the possible important role of BRAF fusion abnormalities in prognosis of subtotally resected pilocytic astrocytomas. The RAS intracellular signaling pathway is an intriguing target, especially utilizing agents that target BRAF and MEK. Increasing information concerning other molecular targets is included.
• Cerebellar astrocytomas are the most common form of childhood low-grade primary intracranial tumors.
• After total resection, over 95% of children with cerebellar astrocytomas are cured.
• Post-surgical adjuvant chemotherapy or radiotherapy is not needed for the vast majority of patients with cerebellar astrocytomas.
Historical note and terminology
Since the mid-1920s, low-grade glial tumors of the cerebellum have been identified as having a more favorable prognosis than other astrocytomas of the central nervous system (Bailey and Cushing 1926). As early as 1931, in a report of 76 cases of cerebellar astrocytoma, Cushing stressed their favorable postoperative outcome and how they differed from cerebral astrocytomas (Cushing 1931). In fact, as late as 1937, Bergstrand suggested that many cerebellar astrocytomas were so histologically benign that they should be considered congenital malformations of the cerebellar leptomeninges, "gliocytoma embryonals," rather than a true malignancy (Ringertz and Nordenstam 1951). This concept has been rejected by other pathologists.
Within the categorization of childhood cerebellar low-grade gliomas, a second subvariety has been identified. Gilles and colleagues, and Gjerris and Klinken, pointed out the differences between the more common classical juvenile or pilocytic cerebellar astrocytoma and the diffuse or Gilles type B lesion (Gilles et al 1977; Gjerris and Klinken 1978). The majority of childhood cerebellar astrocytomas are pilocytic astrocytomas (Louis et al 2007).
The 2017 revised WHO classification of tumors of the central nervous system recognizes pilocytic astrocytomas as a distinct entity, but does not subdivide tumors further on molecular findings or tumor location (Louis et al 2016).
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