Oral malignant melanoma arises from melanocytes, the pigment-producing cells found in the lining of the mouth. It is the most common malignant tumour of the oral cavity in dogs and is among the most aggressive cancers encountered in canine oncology. The tumour can appear as a pigmented (dark) or amelanotic (non-pigmented) mass on the gums, palate, tongue, or lips. It typically invades underlying bone and spreads early to regional lymph nodes and lungs — by the time of diagnosis, metastasis has often already occurred. The WHO staging system, based on tumour size, is one of the strongest predictors of survival. Treatment usually involves aggressive surgery, often requiring partial removal of the jaw. A melanoma vaccine (Oncept) is available and is used as an adjunct to surgery and other treatments, though its precise survival benefit continues to be studied.