Given the importance of the MAPK/ERK pathway activation in melanoma development, we examined the levels of the activated (phosphorylated) ERK1/2 (P-ERK1/2) in primary cutaneous melanoma tumours from Grey (n = 19) and non-Grey (n = 12) horses of different breeds from three geographic locations across Europe by indirect immunofluorescence, using an anti-MITF antibody to mark melanocytic lineage [23]. Here, MITF is linked to cutaneous melanoma.