The histological characteristics of LGGs are diverse, and approximately 31.1% of these lesions consist of low-grade astrocytomas, oligodendrogliomas, and ependymomas. There are also LGGs of mixed histological characteristics of which oligoastrocytoma occurs most commonly. Although some LGGs such as pilocytic astrocytomas and ependymomas show limited infiltrative growth, most of these lesions diffusely invade brain tissue. The prognosis and treatment for these infiltrating LGGs have been the subject of much controversy in the literature. Patient age, presence of neurological deficit, tumor size and extension across the midline, and histological subtype (in particular, the presence of an oligodendroglioma component) appear to be the most important prognostic factors.2,17 Overall median survival in patients with infiltrative LGGs is between 3 and 9 years.17,18
Infiltrative LGGs are known to dedifferentiate to more aggressive histological characteristics. The incidence of malignant tumor transformation in various clinical series has ranged from 13 to 86%.1,10,12,13,15,16 In many of these studies, however, malignant transformation is not well documented. Deficiencies in histological data from repeated surgeries and substantial differences in tumor grading systems that define permissible anaplastic features for the diagnosis of an LGG may account for the wide range of transformation rates. In addition, many of these patients received radiation therapy and/or chemotherapy, which may have interfered with histological interpretation and confounded the natural progression of the LGG.
The aim of this study was to determine the rate of and factors influencing tumor progression as well as to analyze malignant transformation in a well-defined cohort of adult patients who had undergone repeated operations without confounding therapy by using a uniform histological grading system in the era of MR imaging.
We acknowledge Kim Yee for technical assistance.
Piepmeier JM: Observations on the current treatment of low-grade astrocytic tumors of the cerebral hemispheres. J Neurosurg 67:177–1811987Piepmeier JM: Observations on the current treatment of low-grade astrocytic tumors of the cerebral hemispheres. J Neurosurg 67:
Shaw EArusell RScheithauer Bet al: Prospective randomized trial of low-versus high-dose radiation therapy in adults with supratentorial low-grade glioma: initial report of a North Central Cancer Treatment Group/Radiation Therapy Oncology Group/Eastern Cooperative Oncology Group study. J Clin Oncol 20:2267–22762002J Clin Oncol 20:
Steiger HJMarkwalder RVSeiler RWet al: Early prognosis of supratentorial grade 2 astrocytomas in adult patients after resection or stereotactic biopsy. An analysis of 50 cases operated on between 1984 and 1988. Acta Neurochir 106:99–1051990Acta Neurochir 106:
This research was supported by the National Institutes of Health Grant No. T32CA09291.
The results of this study were presented in part at the scientific session of the American Association of Neurological Surgeons meeting in Toronto, Ontario, Canada, April 2001.