Incidence of malignant tumours in patients with a non-functioning pituitary adenoma

Whether patients with non-functioning pituitary adenoma (NFPA) are at increased risk of developing malignant tumours has been sparsely studied and is a matter of debate. In this study, we have investigated the incidence of malignant tumours in a large and unselected group of patients with NFPA. The study was nationwide and included all patients diagnosed with NFPA between 1987 and 2011 (n = 2795) in Sweden, identified in the National Patient Register. Malignant tumours, occurring after the NFPA diagnosis, were identified in the Swedish Cancer Register between 1987 and 2014. Standardised incidence ratios (SIRs) for malignant tumours with 95% confidence intervals (CI) were calculated using the Swedish population as reference. In total, 448 malignant tumours were detected in 386 patients with NFPA, as compared to 368 expected malignancies in the general population (SIR 1.22 (95% CI 1.11-1.33)). The incidence of neoplasms of the brain was increased (SIR 5.83 (95% CI 4.03-8.14)). When analysing the total incidence of malignancies excluding neoplasms of the brain, the overall SIR was still increased (SIR 1.14 (95% CI 1.03-1.26)). The incidence of malignant neoplasm of skin other than malignant melanoma (SIR 1.99 (95% CI 1.55-2.52)) and malignant melanoma (SIR 1.62 (95% CI 1.04-2.38)) were increased, whereas the incidence of breast cancer (SIR 0.65 (95% CI 0.42-0.97)) was decreased. The incidence of other types of malignancies did not differ significantly from the expected incidence in the general population. In conclusion, patients with NFPA have an increased overall risk of developing malignancies. To what extent these findings are due to more frequent medical surveillance, genetic predisposition or endocrine changes, remains unknown.