OTHR-17. A Unique Case of Pediatric Meningeal Melanocytoma with Malignant Transformation to Meningeal Melanoma

Background Meningeal melanocytomas (MM) are rare primary melanocytic tumors of the leptomeninges that almost exclusively occur in adult populations with rare malignant transformation to meningeal melanoma. Clinical Case: A 14 year old male presented with right ear fullness and was found to have multifocal brain masses, including in the internal auditory canals, initially thought to be consistent with NF2-related schwannomatosis and treated with bevacizumab. However, germline NF2 testing was negative. A year later, he was found to have new spinal involvement and underwent surgery due to wrapped tumor around the basilar artery with surgical pathology consistent with meningeal melanocytomas positive for GNA11 mutation. Over the course of the next three years, he received multiple courses of radiation therapy, selumetinib, everolimus, and bevacizumab with repeated tumor progression although good overall clinical status. Repeat biopsy four years after initial diagnosis in the setting of more rapid clinical worsening demonstrated progression to meningeal melanoma with a new BAP1 mutation. He was started on checkpoint inhibitor treatment with nivolumab/ipilimumab and then the PARP inhibitor olaparib due to BAP1 mutation, along with cranial radiation. Despite aggressive treatment, he continued to have tumor progression and succumbed to the disease approximately five years after initial presentation. Conclusions This case demonstrates a unique presentation of MM in a pediatric patient with malignant transformation to meningeal melanoma, rare even in adult populations, with malignant transformation found to occur in less than 5% of patients with MM. Our patient’s melanoma was recalcitrant to multiple of lines of therapy, similar to previous studies demonstrating limited response to adjuvant chemotherapy or immunotherapy. Thus, understanding the factors that cause malignant transformation in addition to better treatment modalities for unresectable MM and meningeal melanomas are needed.