Melanoma (Canine)

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Melanoma is a type of cancer in dogs. It may develop anywhere but is commonly found in the mouth, toes, behind the eyes or on the skin of dogs. It can be benign or malignant. Melanoma arises from melanocytes which are cells that give pigment or color to the skin. Usually skin melanomas are benign. Tumors found in the mouth, toes, or eyes tend to be malignant. The melanomas may be pigmented or unpigmented, which does not affect prognosis. In dogs, tumors are usually solitary and are brown to black in appearance.

Symptoms in dogs of oral melanomas include increased salivation and saliva streaked with blood, bad mouth odor, and difficulty eating with weight loss. Oral melanomas can affect surrounding tissue and commonly spread to lymph nodes and lungs at the time of initial diagnosis. If a toe is involved the dog may limp.

Common name: Canine melanomas, Oral melanomas
Scientific name: Oral melanocytic tumors, skin and digit melanocytic tumors

Diagnosis

Signalment
Melanomas occur more commonly in dogs and cats more than 10 years of age. Breed predilection in dogs suggests a genetic basis. Breeds reported to be at risk include Scottish terriers, Boston terriers, Airedale terriers, cocker spaniels, boxers, Springer spaniels, Irish setters, Irish terriers, chow chows, Chihuahuas and Doberman pinschers.

Incidence/prevalence
Oral malignant melanomas comprise about 30-40% of all malignant tumors in dogs, and occur most frequently in older, smaller, male dogs.

Geographic distribution
Canine melanoma is found worldwide.

Clinical signs (primary most to least frequent, scientific term, synonyms),
Slow or rapidly growing mass, lameness if tumor involves a digit, excessive salivation, halitosis (bad breath), bloody oral discharge, difficult eating and swallowing, weight loss

Clinical signs (secondary most to least frequent, scientific term, synonyms),
Coughing, dyspnea (difficult breathing)

Cause (scientific, common term),
The cause of canine melanoma is unknown.

Organ system affected (most to least affected),

Skin, oral cavity, lymph nodes, lungs

Diagnostic tests

Complete blood count, serum biochemistry test, urinalysis, chest and abdominal radiographic views, biopsy with histopathological examination, fine needle aspiration of lymph nodes or solid tumors, computed tomography (CT scan)

Differential Diagnosis

Mast cell tumor, lymphosarcoma, carcinoma, epulis, abscess, benign polyp

Overview

Melanoma is a type of cancer that arises from melanocytes which are cells that give pigment or color to the skin. Tumors may develop anywhere but are most commonly found in the mouth, toes, behind the eyes or on the skin of dogs. Melanoma can be benign or malignant. Usually skin melanomas are benign. Tumors found in the mouth, toes, or eyes tend to be malignant. The melanomas may be pigmented or unpigmented, which does not affect prognosis. In dogs, tumors are usually solitary and are brown to black in appearance.

Symptoms in dogs of oral melanomas include increased salivation and saliva streaked with blood, bad mouth odor, and difficulty eating with weight loss. Oral melanomas are locally invasive, commonly spread to lymph nodes and are often present in lungs at time of initial diagnosis. If a toe is involved the dog may limp.

Oral malignant melanomas comprise 30 to 40% of all malignant tumors in dogs, and occur most frequently in older, smaller male dogs. Breed predilection in dogs suggests a genetic basis. Breeds reported to be at risk include Scottish terriers, Airdales, Boston terriers, cocker and Springer spaniels, Boxers, Irish setters and Irish terriers, Chow chows, Chihuahuas and Doberman pinschers.

Treatment

Home Care
Annual visits to a veterinarian for a full physical exam are recommended to identify abnormal growths. Veterinarians will recommend tests to reach a diagnosis and initiate appropriate care for skin or oral tumors that are identified.

Professional Care
Veterinarian will take a complete medical history, perform a physical examination, and do tests including blood work, urinalysis, chest and abdominal radiographic (x-ray) views. A fine needle aspiration and biopsy will confirm the diagnosis of canine melanoma. Standard treatment for skin and oral melanomas is removal of the tumor by surgery. Chemotherapy and radiation therapies are also useful for treating dogs for oral melanomas and may shrink skin melanomas that cannot be removed surgically.

Recently, a vaccine to treat canine melanoma was approved by U.S. Department of Agriculture. The vaccine will only be available from veterinary oncology (cancer) specialists for clinical trials. Consultation with a board-certified veterinary oncologist is warranted.

Action
Diagnosis and treatment should be done by a veterinarian. If started early, treatment involving surgery and radiation may improve the disease-free interval and long-term survival.

Outcome
Melanoma is the most malignant of all skin cancers in dogs and therefore has the poorest prognosis. The prognosis for malignant melanoma arising from skin is generally more favorable than with oral melanomas. Benign skin tumors removed surgically have a much better prognosis than malignant tumors which often recur or metastasize.

If found in the mouth, the prognosis is worse. Only 25% of dogs diagnosed with oral melanomas will survive one year. The future does offer hope. Clinical trials using the new vaccine demonstrated significantly longer life spans, even in dogs with advanced staged melanoma.

References/Additional Readings
Ettinger, S.J. & Feldman E.C. Textbook of Veterinary Internal Medicine: Elsevier Saunders Volume 1 and Volume 2, 2005; 6th edition; 1290-1294.

Bonagura, J.D. & Kirk, R.W. Kirk's Current Veterinary Therapy XII; W.B. Saunders Company, 1964; 514-693.

Tilley, LP. and Smith, WK. In: The 5-Minute Veterinary Consult, Lippincott Williams and Wilkins, 2004, 3rd edition; 824-827.

Author
Geruza Paiva, DVM

Editor
Sharon Gwaltney-Brant, DVM, PhD, DABVT, DABT

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