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[astro- + cyt- + -oma]
Tumor of the brain or spinal cord composed of astrocytes. Tumors are graded according to how many mitoses are found in a biopsy specimen, how necrotic they are, and how aggressively they invade surrounding tissues, esp. blood vessels. The least invasive of these tumors are known, according to the World Health Organization (WHO) grading system as (grade I) pilocytic astrocytomas, pleomorphic xanthoastrocytomas, and subependymal giant cell astrocytomas. The average survival for patients with grade 1 astrocytoma is about a decade. The most aggressive (grade IV) astrocytomas are called glioblastoma multiforme. These tumors have a poor prognosis, typically less than a year.

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