Risk of malignancy after gamma knife stereotactic radiosurgery.
To assess the risk of radiosurgery to cause malignant transformation in benign tumors or to induce new malignancies. A retrospective cohort study comparing the Sheffield, England, radiosurgery patient database with national mortality and cancer registries. This data set comprises approximately 5000 patients and 30,000 patient-years of follow-up, with more than 1200 patients having a follow-up period longer than 10 years. In this material, a single new astrocytoma was diagnosed, whereas, based on national incidence figures, 2.47 cases would have been predicted. No increased risk of malignancy was detected in this series, supporting the safety of radiosurgery. Pragmatically, in advising patients, the risks of malignancy would seem small, particularly if such risks are considered in the context of the other risks faced by patients with intracranial pathologies requiring radiosurgical treatments.