Fig. 1

Examples of SF3B1 mutation in a primary leptomeningeal melanocytoma and intermediate-grade melanocytic tumor. a. Hematoxylin-and-Eosin (H&E) staining of the melanocytoma of patient #4 showing round to oval, slightly pleomorphic, vesicular nuclei, often with a prominent nucleolus, and with dispersed melanin pigment in the cytoplasm of the tumor cells. b. BAP1 immunostaining of this melanocytoma revealed heterogeneous staining of the tumor cell nuclei, the majority of these nuclei being positive. The arrows indicate nuclear staining in endothelial cells. Note that the tumor cells also show variable cytoplasmic staining. c. H&E staining of the intermediate-grade melanocytic tumor of patient #18 showing a proliferation of spindle cells with invasion in glial tissue (at the right). d. BAP1 immunostaining of the tumor depicted in (c) reveals positive nuclei in more than 90 % of tumor cells. The arrows indicate nuclear staining in endothelial cells. e. Forward sequence tracing surrounding codon 634 of SF3B1 showing the c.1900G > A (p.(Val634Ile)) mutation detected in the tumor depicted in (a) and (b). f. Forward sequence tracing surrounding codon 625 of SF3B1 showing the c.1873C > T (p.(Arg625Cys)) mutation present in the tumor depicted in (c) and (d)