Canine Oral Malignant Melanoma

Canine Oral Malignant Melanoma

Key Points

  • Oral malignant melanoma (OMM) is the most common malignant oral tumor in the dog
  • Overrepresented breeds include Chow Chows, Golden Retrievers, Poodles, and Cocker Spaniels

Pathology and Natural Behavior

  • Melanoma- tumor of melanocytes
  • About 1/3 of OMM are amelanotic and may not contain any melanin
  • Diagnostic challenge
    • Morphologically, OMM can look like neoplasms of mesenchymal (sarcoma), epithelial (carcinoma), or round cell origin
    • May be difficult to diagnose if they are amelanotic
  • The majority of OMM are metastatic (up to 80%)
    • Frequently metastasize to local lymph nodes and then the lungs
  • Besides the oral cavity, other common places for melanoma to occur include:
    • Cutaneous (more commonly benign)
    • In nail beds (about 50% are malignant and 50% are benign)

Diagnosis and Staging

  • Biopsy is needed to definitively diagnose OMM
    • Can distinguish from common oral tumors (i.e. squamous cell carcinoma or fibrosarcoma)
  • Once a diagnosis is obtained, staging should include:
    • Minimum database
    • Regional lymph node aspirates
    • Thoracic radiographs
  • Cross sectional imaging with CT or MRI are often helpful for assessing bone involvement and surgical planning


  • Treatment of choice for the primary tumor is surgical excision with wide margins, which usually necessitates removal of underlying bone (partial mandibulectomy or maxillectomy)
  • Radiation therapy is useful in shrinking the tumor or temporarily slowing its growth if surgical excision is not an option or if there is high chance of local recurrence
  • Adjuvant systemic therapy in the form of chemotherapy or immunotherapy are additional treatment options which may help to slow the progression of, or to shrink metastatic disease
    • The platinum agents, carboplatin and cisplatin, have shown mild efficacy in shrinking gross OMM lesions temporarily


  • Melanoma is often an immunogenic tumor and many forms of immunotherapy have been attempted
  • Currently, a xenogeneic human DNA vaccine is commercially available for use in dogs with OMM
  • The vaccine is to be used for treatment of OMM after it has developed, NOT to prevent the disease from developing as with traditional vaccines
  • How the vaccines works:
    • Injected DNA encodes for a human protein called tyrosinase, which is found in melanocytes and melanoma cells
    • Since tyrosinase is a human protein, the canine immune system recognizes it as a foreign antigen and mounts an immune response by forming antibodies against it
    • Similarities between human and canine tyrosinase cause the antibodies to cross react and bind with canine tyrosinase as well, creating an immune response to the melanoma cells
  • Early reports of the vaccine showed some promise but its efficacy remains to be proven and requires further investigation


  • Variables with prognostic significance include:
    • Tumor size: tumors <2cm have a median survival time of about 17 months, >2cm have a median survival of about 5.5 months
    • Clinical stage
    • Complete margins obtained with the first surgery
    • Tumor location: dogs with tumors in the rostral oral cavity have longer median survivals than those in the caudal oral cavity
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