Malignant melanoma is a tumor arising from melanocytes, which are the cells that produce pigment. There is no known cause of malignant melanoma. It is seen more commonly in dogs than cats and primarily affects middle-aged to older pets.
Malignant melanoma can originate from different areas in the body, most often the oral cavity, skin, and digits. The aggressiveness of the tumor and the likelihood of the metastasis vary with the tumor location. Any organ may be affected by a metastatic melanoma (tumor that has spread from a primary site).
What to Watch For
Tumors occur most commonly in the skin, digits and in the mouth. The tumors may be pigmented (black) or unpigmented. Solitary (single) growths that may or may not be pigmented or dark in color, most commonly on the face, truck, feet, and scrotum
In patients with cutaneous melanoma:
In patients with the oral form:
Halitosis (bad breath)
Bleeding from the mouth
Patients with advanced disease may experience difficulty breathing due to metastasis (spread) to the lungs.
Diagnosis A complete blood cell count (CBC), biochemical profile, and urinalysis should be performed in all cases, and are most often within normal limits.
Screening chest X-rays, although often within normal limits, may be of benefit in older patients, and/or may reveal evidence of pulmonary (lung) metastasis.
Fine needles aspirates retrieve cells for analysis with a small needle and syringe and may be helpful in diagnosing malignant melanoma.
Evaluation of the associated lymph nodes by fine needle aspirate/cytology is recommended as well.
Abdominal ultrasound may be indicated in patients with lesions that occur in or on the hind legs.
Biopsy of the mass is necessary for a definitive diagnosis of malignant melanoma.
Additional tests to help determine the type of tumor or the overall malignancy. Tests may include immunohistochemical staining may confirm the type of tumor or evaluation of the mitotic index may help determine the malignancy associated with that particular tumor.
Treatment Treatment of choice is surgical removal of the tumor.
Melanoma involving the nail bed or digit often requires amputation of the digit.
Melanoma involving the oral cavity often necessitates radical mandibulectomy, or removal of the a part of the associated lower jaw, or maxillectomy, which is the removal of the part of the associated upper jaw.
Adjunctive (concurrent) chemotherapy is recommended if surgical excision is incomplete or the mass cannot be removed surgically.
Radiation therapy may of benefit in certain cases.
Immunotherapy to regulate the immune system may be of benefit in selected cases.
Home Care and Prevention
Prognosis is generally guarded and early detection is very important. Those occurring in the scrotum, digit, or oral cavity are most often malignant. It is estimated that most oral melanomas are malignant and 60% are metastatic. Approximately 30 to 60% of nail bed tumors are metastatic. Aggressive and radical surgery greatly increases survival times and decreases reoccurrence rates.
Contact your veterinarian if there is recurrence of the melanoma or change at the surgical site. Return for follow up as directed by your veterinarian.
There is no preventative care for malignant melanoma.