Is Radiation Necrosis in Radiated Melanoma Brain Metastasis Increasing Because Immunotherapy is Contributing to This or Are Patients Just Living Longer?

e21518 Background: The use of immune checkpoint inhibitors, particularly combination ipilimumab and nivolumab, has drastically changed the management of patients with melanoma brain metastasis. Select patients also benefit from brain-directed stereotactic radiation. Radiation necrosis is a risk associated with stereotactic radiation that oncologists have been observing more frequently in the era of immunotherapy. Methods: Patients were identified who had a history of metastatic melanoma treated with stereotactic brain radiation who subsequently developed radiation necrosis. Brain tissue from those patients with a subsequent resection of their radiation necrosis was obtained and examined for immune infiltrate and other factors. The tissue obtained was evaluated by blinded pathologists who graded % viable tissue, % necrosis, % tumor and % fibrosis. In addition, they graded inflammation on a scale of 1-3. Results: Seven patients were identified who had surgery for radiation necrosis following radiation to melanoma brain metastasis. Tissue was available for five patients. Two patients had received no prior immunotherapy, one patient had received ipilimumab and two patients received combination ipilimumab and nivolumab. The samples obtained consisted of almost entirely viable brain tissue or necrosis. There was minimal inflammation seen in all patients’ samples including those who had not received immunotherapy and those who had. Conclusions: Radiation necrosis in patients on immunotherapy who receive brain-directed stereotactic radiation is a rising problem. On pathologic evaluation increased immune infiltrate is not observed in patients on immunotherapy with radiation necrosis compared to those who never received immunotherapy. This suggests that the increased rates of radiation necrosis may be more likely associated with longer survival as opposed to a direct causative effect from the immunotherapy although with our limited sample size this will need further exploration.[Table: see text]