A cumulative risk of tumour induction inside the brain after surgery and radiation thera-py of 1.3% (95%CI: 0.4-3.9%) to 2% (95%CI: 0.9-4.4%) over the first 10 years, and of 1.9% (95%CI: 0.7-5%) to 2.4% (95% CI: 1.2-5%) over the first 20 years has been reported68,69. The relative risk of a secondary brain tumour as compared to the incidence in the normal population is 9.4. The median time to detection is 7 years for glioma, 9.7 years for sarcoma and 13.8 years for meningioma.
However, no firm support for an increased incidence of a second brain tumour is found by others in a cohort of 279 NFA patients treated between 1931 and 1988. Two astrocytomas – 7 and 24 years after irradiation – and one meningioma – 19 years after irradiation – were found (RR 2.7: 95%CI; 0.6-7.8) 70.
A genetic trait that predisposes to both pituitary tumours and brain tumours is an alternative causal factor. To support this idea, there are reports of the co-occurrence of meningioma and pituitary adenoma in non-irradiated patients71. Radiation-induced meningiomas differ from “spontaneous meningiomas” in location, multiplicity and aggressive biological behaviour72.
There is no evidence that cranial irradiation per se is the causal factor. A cohort study of non-irradiated pituitary tumour patients, who have the same initial malignancy, is needed.