PS1 - 140 The Effect of Timing of Stereotactic Radiosurgery Treatment of Melanoma Brain Metastases Treated with Ipilimumab

Melanoma represents the third most common cause of CNS metastases. Immunotherapy has evolved as a treatment option for patients with stage-IV melanoma. Stereotactic radiosurgery (SRS) also elicits an immune response within the brain and may interact with immunotherapy. We report a cohort of patients treated for brain metastasis with immunotherapy and evaluate the effect of SRS timing on the intracranial response. Methods: All consecutively treated melanoma patients receiving Ipilimumab and SRS for their brain metastasis were included in the retrospective analysis. 46 patients harboring 232 brain metastases were reviewed. The median clinical follow-up was 7.9 months (3-42.6). Median age was 63 years (24.3-83.6). 32 patients received SRS before or during ipilimumab cycles (Group-A) whereas 14 patients received SRS after the ipilimumab treatment (Group-B). Radiographic and clinical responses were assessed at approximately 3 months intervals after SRS. Results: The two cohorts were comparable in pertinent pre-treatment aspects with the exception of SRS timing relative to ipilimumab. Local recurrence free duration (LRFD) was significantly longer in Group-A patients (19.6 months, range 1.1-34.7 months) as compared to group-B patients (3 months, range 0.4-20.4 months), respectively (p=0.002). Post-SRS perilesional edema was more significant in Group-A. Conclusions: The effect of SRS and ipilimumab in attaining LRFD seems greater when SRS is performed before or during ipilimumab treatments. The timing of immunotherapy and SRS may effect LRFD and post-radiosurgical edema. The interactions between immunotherapy and SRS warrant further investigation so as to optimize the therapeutic benefits and mitigate the risks associated with multimodality, targeted therapy.