Treatment One of the more interesting developments in the treatment of low-grade cerebral tumors has been the comparison made by Jakola and colleagues between the practices in two Norwegian centers, one which practiced an aggressive approach of removing accessible tumors when they are discovered, and another, of observing the patient by sequential imaging to determine if the tumor has transformed into a more aggressive mode. While a small, and not a randomized trial, surgical excision resulted in longer survival. Excision of part of a cerebral astrocytoma can improve survival in a good functional state for many years. Modern techniques of brain mapping have allowed larger and probably safer resections of these tumors. An example of this has been offered by Sanai and colleagues, who performed mapping of language areas in a large consecutive series of glioma patients.
The cystic astrocytoma of the cerebellum is relatively benign in its overall behavior. In such cases, resection of the tumor nodule is of singular importance in delaying or preventing a recurrence. In clinical series, the rate of survival 5 years after successful surgery has been greater than 90 percent (Pencalet et al). The outcome is less ensured when the tumor also involves the brainstem and cannot be safely resected.
The natural history of the low-grade gliomas is to grow slowly and eventually undergo malignant transformation. The duration of progression before this transformation occurs and the latency to recurrence with modern treatment may extend for many years. A survey of the outcome of these low-grade supratentorial tumors showed that 10-year survival after operation was from 11 to 40 percent provided that conformal therapy (focused on the tumor, in contrast to whole brain radiation) 5,300 cGy was given postoperatively (Shaw et al). This, of course, is quite in contrast to the figures for glioblastoma. Repeated operations prolong life in some patients.
In younger patients, particularly if the neurologic examination is normal or nearly so, radiation can be delayed, and the status of the tumor can be evaluated by serial imaging. A number of studies have come to the conclusion that delaying radiation in younger patients may avoid the consequences of dementia and hypopituitarism (Peterson and DeAngelis), but others have suggested that the tumor itself and antiepileptic drugs cause more difficulty than high-dose radiation. An extensive randomized trial of early radiotherapy in adults demonstrated that median progression-free survival was extended to 5.3 years by early treatment in comparison to 3.4 years for observation only and radiation treatment that was initiated when signs of progression occurred, but that overall survival was unaffected, averaging just over 7 years in both groups (van den Bent et al). Lacking any clear benefit on survival, it seems to us that radiation may be withheld initially. An increase in seizures or worsening neurologic signs then presses one to turn to radiation or further surgery.
Although chemotherapy has an ambiguous place in the treatment of low-grade pure astrocytomas, tumors with an oligodendroglial component respond well to combination chemotherapy used for the treatment of anaplastic oligodendroglioma. One randomized trial has shown a modest benefit in overall survival by adding chemotherapy (procarbazine, CCNU, vincristine; termed PCV) to radiation therapy of the brain (13.8 years median survival vs 7.8 years; see Buckner et al). Temozolomide has replaced PCV in many centers.
The special features of astrocytomas of the pons, hypothalamus, optic nerves, and chiasm, which produce highly characteristic clinical syndromes and do not behave like a cerebral mass, are discussed further on in this chapter.