Outcomes of melanoma brain metastases treated with stereotactic radiosurgery with and without concurrent immune checkpoint therapy.

Abstract

e21026 Background: Evidence supports a synergistic effect between immunotherapy and radiotherapy. In this single-institution study, we compared outcomes of patients (pts) with melanoma brain metastases (BMs) who received Gamma Knife Radiosurgery (GKRS) with and without concurrent immune checkpoint blockade (ICB). Methods: Using an IRB-approved protocol, we identified pts with melanoma BMs who received GKRS from 5/2000 to 8/2016. Treatment was deemed concurrent if patients had GKRS within 4 weeks of ICB. Irradiated lesion control, tumor growth rate (TGR; percent change in product diameters per month), distant brain control, overall response rate (ORR) by modified WHO criteria, best response, and overall survival (OS) were compared. Results: 28 pts were identified: 17 (34 BMs total) received GKRS alone; 11 (23 BMs total) received concurrent GKRS/ICB. ICB included: ipilimumab (n = 3), anti-programmed death-1 (anti-PD-1) therapy (n = 4), and combined ipilimumab + nivolumab (n = 4). In comparing baseline characteristics between the GKRS alone and GKRS/ICB groups: median age was 65 v. 59 years, proportion of males was 53% v. 73%, 41% v. 45% had prior neurosurgery, and median number of prior systemic therapies was 1 v. 0. There was no difference in irradiated lesion control (6-month control rate 86% v. 96%; n = 57; p = 0.65), median TGR (-14% [range -100% to +61%] v. -20% [range -71% to 0%]; n = 42 lesions, p = 0.38), or distant brain control (6-month control rate 68% v. 60%; p = 0.51; median follow-up 8.6 months v. 8.0 months) with GKRS/ICB v. GKRS alone. The ORR with GKRS alone v. GKRS/ICB was 61% v. 47% (p = 0.33), and the median maximum reduction in BM bidimensional measurement was -69% v. -45% (p = 0.43). Median OS from the date of GKRS was not reached for the GKRS/ICB group and was 16.6 months for the GKRS alone group (p = 0.03). Conclusions: There was no difference in local lesion control, TGR, or distant brain control with concurrent GKRS/ICB compared to GKRS alone, but the study was limited by small patient numbers and biased by closer follow-up in the GKRS/ICB group. OS was longer with concurrent ICB, likely reflecting the survival improvement with immune checkpoint inhibitors.