Evaluation of radiotherapeutic and immune-modulatory response to whole brain radiotherapy or stereotactic radiosurgery in patients with brain metastases from malignant melanoma treated with or without ipilimumab (ELEKTRA).

e14104 Background: Immune checkpoint blockers have dramatically improved the survival of patients (pts) suffering from advanced metastasized melanoma. In pts with melanoma brain metastases (MBM) a combination with radiotherapy (RT) is routinely used. Methods: We prospectively included 106 pts with MBM in a non-randomized observational trial with 7 treatment cohorts. Patients in cohort 1-4 were treated with ipilimumab (+/- nivolumab) and either stereotactic (up to 3 MBM) or whole brain RT (≥ 4 MBM) before or after the start of immunotherapy. Cohort 5 and 6 included pts who received RT with an ipilimumab-free systemic treatment and cohort 7 pts were treated with ipilimumab (+/- nivolumab) and no RT. Primary endpoints were immunological response in the peripheral blood (FACS of T cell subsets, ELISpots against melanoma antigens) and radiological response, secondary endpoints were progression free and overall survival. Results: Included pts were in median 61 years old, 72% were male. At trial inclusion, 31% of pts had an elevated LDH. 39% of ipilimumab treated pts received combination therapy with nivolumab. Clinically, ipilimumab treated pts in the early RT groups had better responses of both intra- and extracranial disease (p = 0.04 for both). Multivariate analyses showed a better PFS for pts with early RT (p = 0.02) and normal LDH (p = 0.049). Type of radiation (p = 0.6) and immune therapy (p = 0.8) had no significant influence in this small cohort of pts. Immune monitoring revealed that ipilimumab leads to an increase in activated CD4+ and CD8+ T cells in the peripheral blood which was maintained in responding pts and higher in pts receiving early RT. Treg were not depleted in general but activated by ipilimumab. However, responders displayed a temporary decrease of Treg and activated Treg under treatment. An increase in the detection of melanoma antigens could be observed after 2 cycles of ipilimumab which was higher in pts with combined radioimmunotherapy compared to ipilimumab only. Conclusions: Preliminary data from this small observational trial might lead to a preference of a treatment sequence with radiotherapy first, followed by checkpoint inhibition in pts with MBM.