ERBB4 and melanoma: Due to the high aggressiveness of canine melanoma and the scarcity of information of association with epidermal growth factor receptors and canine melanoma progression, the aims of the present study were to characterize the expression of EGFR, HER2, HER3 and HER4 in skin and oral canine melanoma and to determine their relationship with the histopathological characteristics and proliferative indices of these tumors.