High-resolution RNA-sequencing reveals TRIM33 :: CSDE1 gene fusion in metastasizing vulvar melanoma

Although mucosal melanomas are rare and constitute approximately 1.4% of all melanomas, the prognosis of patients with mucosal melanoma is poorer in comparison to cutaneous melanomas. Despite their poor prognosis, limited treatment options are currently available for patients with advanced disease. These noncutaneous subtypes of melanomas are not responding to treatment used for cutaneous melanomas. We performed RNA sequencing on four mucosal melanoma samples comprising of two primary tumors and two corresponding metastases. A TRIM33 :: CSDE1 fusion was detected in both the primary tumor and metastasis of a vulvar melanoma, supporting the fusion to be a driver in oncogenesis. Vulvar melanoma is the third tumor to have been reported to harbor TRIM33 :: CSDE1 fusion. Detecting fusions may have a clinically significant impact in patients with advanced mucosal melanoma who have failed front-line immunotherapy.