a) Case 1 – A monomorphous population of slightly spindled, amelanotic cells in vaguely whorling array is present (hematoxylin-eosin, x100). Inset - Diffuse cytoplasmic immunolabeling for HMB-45 confirms the melanocytic nature of the tumor cells (immunoperoxidase with hematoxylin counterstain, x100). b) Case 1 - sequencing electropherogram of the tumor (upper panel) shows a homozygous point mutation (arrow) in exon 4 of GNAQ; the corresponding region of the reference sequence is illustrated in the lower panel [nucleotide assignment: A=green; C=blue; G=black; T=red]. c) Case 2 – Spindled and pigmented tumor cells are present, some of which whorl about a blood vessel (hematoxylin-eosin, x100). d) Case 2 - sequencing electropherogram of the tumor (upper panel) shows a heterozygous point mutation (arrow) in exon 5 of GNA11; the corresponding region of the reference sequence is illustrated in the lower panel [nucleotide assignment: A=green; C=blue; G=black; T=red].