LAUSR

and check for possible sequencing errors. We detected 29 somatic mutations, including a recurrent somatic R625C mutation in SF3B1 (frequency, 43.9%). Hotspot neomorphic SF3B1 mutations have been identified in uveal melanoma and subsequently in mucosal melanoma [1, 4]. SF3B1 encodes a component of the spliceosome that regulates RNA splicing and is the most frequently mutated component of the spliceosome in cancer [5]. Dysregulated alternative splicing plays important roles in tumourigenesis and resistance to therapy [5]. SF3B1 mutation induces subtle but broad changes in gene expression and splicing across multiple pathways in chronic lymphocytic leukaemia patients [6]. Such patients have been shown to have faster disease progression and poorer prognosis. SF3B1 is mutated in 18.6% of uveal melanoma, and less than 1% in cutaneous melanoma [1]. We have performed whole-exome sequencing in two mucosal melanoma patients including a 43-year-old man with metastatic melanoma from gingival mucosal melanoma. Previous data [1, 4, 7] and our own data reveal recurrent somatic SF3B1 mutations in 15 of 42 (35.7%) mucosal melanoma patients, suggesting that neomorphic SF3B1 mutations are critical for the occurrence and development of mucosal melanomas. SF3B1 mutation is possibly the driver mutation in mucosal melanoma. In uveal melanoma, GNAQ and GNA11, with somatic mutations, are the driver genes, and somatic BAP1, SF3B1, and EIF1AX mutations occur during tumour progression [8]. GNAQ and GNA11 mutations are mutually exclusive with each other, and BAP1, SF3B1, and EIF1AX mutations occur in an almost mutually exclusive manner [8]. Mutation of the driver genes GNAQ and GNA11 is not associated with prognosis, whereas the secondary mutated genes of BAP1, SF3B1, and EIF1AX are prognostically significant [8]. BAP1 mutation is considered a poor prognostic factor, while SF3B1 and EIF1AX mutations are considered good prognostic factors [8]. Future studies should focus on patients with mucosal melanoma in order to evaluate the contribution of neomorphic SF3B1 mutation to tumorigenesis and investigate why mucosal melanoma is associated with a poor prognosis.