1Low-Grade Gliomas in Adults作者：Jeanine T. Grier, Tracy Batchelor【关键词】 Low-grade,gliomaKey Words. Low-grade glioma ; Astrocytoma ; Oligodendroglioma ABSTRACT Low-grade gliomas are a heterogeneous group of neoplasms usually encountered in younger patient populations. These tumors represent a unique challenge because most patients will survive a decade or more and may be at a higher risk for treatment-related complications. Clinical observations over the years have identified a subset of low-grade gliomas that tends to manifest more aggressive clinical behavior and require earlier, more aggressive 2intervention. Clinical and molecular parameters may allow better assessment of prognosis and application of risk-adjusted management strategies that may include resection, radiation, or chemotherapy. Improved methods of long-term cognitive and functional assessment are desperately needed in this patient population. INTRODUCTION Tumors of the central nervous system (CNS) are grouped according to their cell of origin and are graded based on standard histopathological features. Gliomas comprise a heterogeneous group of neuroectodermal tumors that arise from the glia, the supporting cells of the CNS. Astrocytes, oligodendrocytes, and ependymal cells are types of glial cells that may give rise to astrocytomas, oligodendrogliomas, and ependymomas, respectively. According to the World Health Organization (WHO) classification, the most commonly accepted grading system for brain tumors, the surgical specimen should be assessed for atypical cells, mitoses, endothelial proliferation, and 3necrosis. Tumors with none of these characteristics are classified as grade 1. The more common gliomas in this class are pilocytic astrocytoma (PA), dysembryoplastic neuroepithelial tumor (DNET), pleomorphic xanthoastrocytoma (PXA), and ganglioglioma. Gliomas that possess only one feature, usually atypical cells, are grade 2. Astrocytoma, oligodendroglioma, and oligoastrocytoma fall into the grade 2 category. These tumors are also termed low-grade astrocytoma, low-grade oligodendroglioma, and low-grade oligoastrocytoma, respectively. A subset of gliomas may have both endothelial proliferation and atypia but are well circumscribed and slow-growing. These tumors are considered to be low-grade gliomas (LGGs) despite their departure from the typical classification scheme. LGG refers to tumors in either the grade 1 or grade 2 categories. Tumors with two or more features are considered malignant and are termed grade 3 or grade 4 gliomas. LGGs include a diverse group of tumors within the brain, brainstem, and spinal cord, with distinct characteristics, patterns of occurrence, response to treatment, and survival. Patients with LGG tend to be young, otherwise healthy 4individuals, and management decisions, such as timing of intervention, extent of surgical resection, timing of radiotherapy, and long-term benefits and risks of chemotherapy, have been controversial. In this review, we outline the key issues of LGG management. For the purpose of this review, LGG refers only to supratentorial nonpilocytic astrocytoma, oligodendroglioma, and mixed oligoastrocytoma. Other subtypessuch as pilocytic astrocytoma, subependymal giant cell astrocytoma, brainstem glioma, and optic nerve gliomahave different clinical presentations, diagnostic algorithms, and treatments. These four subtypes are briefly discussed at the end of this review. INCIDENCE An estimated 43,800 new cases of primary CNS tumors were diagnosed in 2005 1. Gliomas accounted for 40% of all these primary CNS tumors 1. Astrocytomas represent 75% of all gliomas, while ependymomas, oligodendrogliomas, and other glioma subtypes comprise the remaining 25%. The International Classification of Diseases for Oncology (ICDO)-3 5does not identify separate histology codes for low-grade gliomas 2. Since no ICDO-3 codes exist for LGG, specific incidence rates for low-grade oligodendroglioma and low-grade astrocytoma are difficult to determine. From a compilation of citations, the American Association of Neurological Surgeons (AANS) estimated that the annual number of pediatric and adult LGG cases diagnosed in the U.S., including pilocytic astrocytoma, diffuse fibrillary astrocytoma, oligodendroglioma, and oligoastrocytoma, is 1,800 3. In adults aged 2034, gliomas account for 45% of all CNS tumors. Astrocytomas as a group account for 18% and glioblastoma accounts for 6% of young adult tumors 1. Incidence rates for glioblastoma, ependymoma, mixed glioma, and oligodendroglioma are over two times greater in whites than in blacks 1. Currently, there is no compelling evidence for a strong association between environmental exposures and glioma development 4. PRESENTATION 6Most patients with LGG present between the second and fourth decades of life, and a seizure is the presenting symptom in 72%89% of patients 512. Mental status changes are present in 3%30% of patients at the t