Intracranial tumours after external fractionated radiotherapy for pituitary adenomas in northern Sweden

Abstract

We analysed the incidence of second primary intracranial tumours in patients with pituitary adenomas treated with radiotherapy compared to the risk of patients not exposed to irradiation and to the general population. Materials and methods. This retrospective cohort study includes 298 patients with pituitary adenomas that received radiotherapy to the pituitary from 1960 to 2007. The patients were recruited from the Cancer Registry of northern Sweden and the local radiotherapy-registry of the University Hospital in Umeå. Only patients with ≥12 months follow-up after diagnosis of pituitary adenoma were included. A cohort of 131 patients with pituitary adenomas not treated with radiotherapy was used as reference. Standard incidence ratios (SIR) between observed and expected number of second primary intracranial tumours were calculated. Results. The median observation time after diagnosis of pituitary adenoma in 298 patients treated with radiotherapy was 14 years, and the total number of person-years at risk was 4 784. Six (2.0%) of the patients developed second primary intracranial tumours between 7 and 31 years after radiotherapy. Two patients had gliomas and four had meningiomas. The expected number of intracranial tumours was 1.15 giving a SIR of 5.20 (95% CI 1.90–11.31). No significant correlations were found between radiation technique or administered dose and the risk of developing a second primary intracranial tumour. The cumulative risk for second intracranial tumours at 10 and 20 years was 1.3%. Patients not treated with radiotherapy were followed 1 601 years and no second primary intracranial tumour occurred. Discussion. The results indicate an increased risk of second primary intracranial tumours in patients treated with radiotherapy for pituitary adenomas, compared to patients not exposed to irradiation and to the general population. Meningiomas were more frequent than gliomas and the median time interval between radiotherapy and second intracranial tumour was 17 years.