Primary leptomeningeal melanoma: the prognostic significance of its genetic signature and embryological origin.

Primary leptomeningeal melanomas are rare, comprising less than one percent of all brain tumours. They are aggressive and radioresistant tumours, with a poor prognosis. The mainstay of treatment is complete surgical resection and chemotherapy with limited success. Distinguishing a primary leptomeningeal melanoma from the more common metastatic disease can be difficult, and often requires the use of ancillary molecular testing. Primary central nervous system melanomas, including uveal melanomas, frequently exhibit mutations in GNAQ and GNA11, rare in the cutaneous and mucosal counterparts.A case of a primary leptomeningeal melanoma of the cerebellopontine angle is described. Molecular studies identified a GNA11 p.Q209L and a KIT p.M541L missense variant, with losses of chromosomes 1p and 3p demonstrated with cytogenetic studies. Complete surgical resection was not possible and leptomeningeal metastatic disease rapidly ensued despite immunotherapy. Further understanding of the molecular signature may translate to improved diagnosis, prognostication and development of targeted therapies.