**2. Literature review**

#### **2.1 Tumor etiology**

Canine oral melanoma is the most frequently diagnosed malignant tumor in dogs [2]. Oral melanoma is associated with a high local infiltration, metastatic rate, and poor prognosis. Biological behavior and presentation of melanoma vary remarkably and are influenced by anatomic site, stage, and histological features [1, 2]. Increasing age, with no relation to sex, is also a determinant for canine oral melanoma aggressiveness [2, 3, 6].

The etiology of canine oral melanoma is multifactorial, including environmental and genetic factors [6]. In cutaneous melanoma, hairy skin and sunlight exposure could be considered risk factors [2]. However, sunlight exposure cannot be considered a risk factor for oral melanoma. Chronic inflammation or trauma, deep bacterial infections, intralesional necrosis, chemical exposure, and burns are factors associated with canine melanoma development [6, 8].

Highly pigmented oral mucosa and purebred dogs, such as Airedale Terrier, Boston Terrier, Boxer, Chihuahua, Chow, Cocker Spaniel, Doberman Pinscher, English Springer Spaniel, Golden Retriever, Irish Setter, Miniature Schnauzer, Scottish Terrier, Poodles, Beauce Shepherds, Rottweilers, and Labrador Retrievers, are predisposed to melanocytic tumors, including oral melanoma [3–5]. This suggests that melanoma in dogs may have genetic factors [7, 8].
