Glioblastoma multiforme after stereotactic radiotherapy for acoustic neuroma: Case report and review of the literature

¹ Arthur and Sonia Labatts Brain Tumor Center, Hospital for Sick Children Research Institute, Toronto, ON M5T-2S8, Canada, and Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, 560029 India
² Department of Pathology, Western Hospital, University Health Network, Toronto, ON, M5T-2S8 Canada
³ Division of Neurosurgery, Western Hospital, University Health Network, Toronto, ON, M5T-2S8 Canada
⁴ Department of Radiation Oncology, Princess Margaret Hospital, University Health Network, Toronto, ON, M5G-2M9 Canada
⁵ Department of Clinical Physics, Princess Margaret Hospital, University Health Network, Toronto, ON, M5G-2M9 Canada
⁶ Arthur & Sonia Labatts Brain Tumor Center, Hospital for Sick Children Research Institute, Toronto, ON M5T-2S8, Canada, and Division of Neurosurgery, Western Hospital, University Health Network, Toronto, ON, Canada

^* To whom correspondence should be addressed. E-mail: Abhijit.Guha{at}uhn.on.ca.

	Abstract

Indications for the use of radiotherapy in the management of a variety of benign intracranial neoplastic and nonneoplastic pathologies are increasing. Although the short-term risks are minimal, the long-term risks of radiation-induced de novo secondary neoplasms or malignant progression of the primary benign tumor need to be considered. There are currently 19 reported cases of tumors linked with stereotactic radiotherapy/radiosurgery, to which we add our second institutional experience of a patient who succumbed to a glioblastoma multiforme (GBM) after stereotactic radiotherapy for an acoustic neuroma (AN). Review of these 20 cases revealed 10 de novo secondary tumors, of which eight were malignant, with six being malignant gliomas. The majority of the cases (14 of 20) involved AN, with most being in patients with neurofibromatosis-2 (NF2; 8 of 14), reflecting the large numbers and long-term use of radiotherapy for AN. Accelerated growth of the primary benign AN, some 2 to 6 years after focused radiotherapy, was found in six of eight NF2 patients, with pathological verification of a malignant nerve sheath tumor documented in most. The exact carcinogenic risk after radiotherapy is unknown but likely extremely low. However, the risk is not zero and requires discussion with the patient, with specific consideration in young patients and those with a cancer predisposition.

Key Words: acoustic neuroma, neurofibromatosis-2, radiation-induced GBM, radiosurgery