Long-term tumor control following repeat gamma-knife radiosurgery of growing pituitary adenomas: a population-based cohort study

Background Gamma Knife radiosurgery (GKRS) is a well-established treatment for residual or growing pituitary adenomas (PAs) post-partial resection. However, some PAs grow even after initial GKRS, for which the efficacy of repeat GKRS is unclear. The primary objective of this study was to determine long-term progression-free survival (PFS) following repeated GKRS in patients with PA. The secondary objective was to determine predictors of tumor progression in these patients. Methods Single-center, population-based consecutive cohort study of patients with recurrent PAs treated with repeated GKRS due to tumor progression between 1999 and 2022 at the Department of Neurosurgery, Karolinska University Hospital, Stockholm, Sweden. PFS and predictors of tumor growth were assessed. Results 23 patients were included, with a median follow-up time of 6.3 years. The 5-year PFS rate was 57%, and the median duration from repeat GKRS to tumor progression was 2.6 years. Tumor growth after repeat GKRS occurred exclusively within the first three years post-treatment. Older age at the time of repeat GKRS was a significant predictor of continued tumor growth (OR 1.09, p = 0.036). Conclusion Repeat GKRS is a feasible treatment alternative for PAs that exhibit growth following initial GKRS.