499 Silent Corticotroph Staining Pituitary Neuroendocrine Tumors: Prognostic Significance in Radiosurgery

Abstract

INTRODUCTION: There is conflicting evidence on the significance of adrenocorticotrophic hormone (ACTH) staining in the prognosis of nonfunctioning pituitary neuroendocrine tumors (NFpitNETs). METHODS: This retrospective, multicenter study included patients managed with SRS for NFpitNET residuals. The patients were divided into two cohorts: 1) silent corticotroph (SC) for NFpitNETs with positive ACTH immunostaining and 2) non-SC NFpitNETs. Rates of local tumor control, as well as the incidence of post-treatment pituitary and neurological dysfunction were documented. Factors associated with radiological and clinical outcomes were also analyzed. RESULTS: The cohort included 535 patients from fourteen centers with 84 (15.7%) patients harboring silent corticotroph NFpitNETs (SCs). At last follow-up, local tumor progression occurred in 11.9% of patients in the SC compared to 8.1% of patients in the non-SC cohort (p = 0.27). No statistically significant difference was noted in new-onset hypopituitarism rates (10.7% vs 15.4%, p = 0.25) or visual deficits (3.6% vs 1.1%, p = 0.088) between the two cohorts at last follow-up. When controlling for residual tumor volume, maximum dose, and patient age and gender, positive ACTH immunostaining did not have a significant correlation with local tumor progression (HR = 1.69, 95% CI = 0.8 - 3.61, p = 0.17). CONCLUSIONS: In contemporary radiosurgical practice with a single fraction dose of 8-25 Gy (median 15 Gy), ACTH immunostaining in NFpitNETs did not appear to confer a significantly reduced rate of local tumor control after SRS.