MAPK3 and neoplasm: To test whether the constitutive ERK1/2 activation was due to the presence of oncogenic mutations commonly associated with ERK1/2 activation in melanocytic neoplasms, we screened the horse cell lines and seven additional GHM tumours for mutations in exons 11 and 15 of BRAF, the full coding regions of N-, K- and HRAS, exon 4 and 5 of GNAQ and GNA11, and exons 9–21 of KIT. In all the genes except KIT, no mutations were found, indicating the wild-type status of the genes in this melanoma type.