Canine Oral Malignant Melanoma

Epidemiology

Canine oral malignant melanoma (COMM) is a neoplasm of melanocytic cells. MM account for 7% of all malignant neoplasms and between 9 to 20% of all skin tumors in dogs. The most frequently affected site is the oral cavity, making COMM the most common oral neoplasm. The site for oral melanomas is the gingiva, buccal or labial mucosa, hard or soft palate and the tongue. COMM are rapidly growing, invasive and potentially metastatic tumors. They often recur after surgical excision and radio- or chemotherapy. COMM tend to metastasize in 70 to 90% of all cases. COMM are most often diagnosed in dogs older than 10 years with a mean age of 11.6 years.

Classification

The World Health Organization (WHO) has developed a scheme for classifying oral melanomas, which was adapted for dogs. The classification of a tumor is based on: de anatomic site of the tumor, the tumor size and the tumor stage. These variables give an impression of the prognosis of COMM.

The tumor size and stage can be subdivided in categories:

• Category 1: Tumor ≤2 cm diameter
• Category 2: Tumor 2–4 cm diameter
• Category 3: Tumor ≥4 cm diameter
• Category 4: Distant metastasis. Distant metastasis has a higher grade than lymph node metastasis.

The tumor stage is subdivided in:

• Stage 1: Tumor ≤2 centimeter in diameter, without lymph node involvement and no proven metastasis
• Stage 2: Tumor 2–4 centimeter in diameter, without lymph node involvement and no proven metastasis
• Stage 3: Tumor ≥4 centimeter in diameter, with or without lymph node involvement and has no proven metastasis or any tumor size with lymph node metastasis
• Stage 4: Proven metastasis, independent of tumor size or lymph node involvement

Materials and Methods: VSSO Symposium 2016

During the VSSO symposium in Napa, California (2016), COMM were discussed. A pre-event enquiry was sent to the VSSO liststerv with questions pertaining to COMM and similar questions were discussed. During the VSSO discussion a maximum of 99 oncology interested veterinary surgeons, including diplomate specialists of the various colleges, were actively involved using live polling. All polling answers were recorded.

Clinical Guidelines Obtained from Discussion

Staging

Of the various staging procedures, distant metastases was recognised as the most important factor to determine prognosis (70%) and only 13% the size of the tumor. If there are no distant metastases, the most important factors were deemed: lymph node involvement (43%), size of tumor (29%) and the resectability of the tumor (26%).

Lymph Node Staging

In case of a COMM, 56% percent of the interviewed would aspirate both mandibular lymph nodes, 24% the ipsilateral lymph node and 15% bilateral mandibular and retropharyngeal lymph nodes.

When asked what lymph node they would routinely remove during surgery, 45% would use advanced diagnostic imaging to determine, 6% used sentinel lymph node determination, 26% removed standard the ipsilateral lymph node, 13% bilateral mandibular and 10% bilateral mandibular and retropharyngeal.

Diagnostic Imaging

If people had to choose between 3-way thoracic radiographs and CT scan of the chest, 78% would prefer a CT. Fifty percent of the active participants additionally perform diagnostic imaging of the abdomen in oral MM patients, either by ultrasound (64%) or CT (36%). CT of the head and neck is seen as the most ideal preoperative staging and preparation technique by 96% of the interviewed.

Therapy for Oral MM

The preferred approach for a large oral MM was wide or radical surgical excision (89%). Radiation as a sole therapy was chosen by 11% of the audience.

Most of the audience (68%) would recut cases that had marginally excised oral mucocutaneous MM after a full diagnostic work up. Fifteen percent would only use adjunctive therapy for these cases.

When asked what the role of radiation therapy was, 77% answered when surgery was not an option and 21% included it in every case after surgery. When asked what adjuvant therapy one preferred after surgical excision, 73% answered immunotherapy, 16% chemotherapy, 7% NSAIDs and 4% radiation therapy.

MM Vaccine

When asked if the audience felt that the current available melanoma vaccine was effective, 58% answered yes. When asked if they use the vaccine, 84% of the audience said yes. Additionally, 55% used it for stage 4 patients. The question, how many vaccines should you give was answered by 38% as many as you can give, >4 doses by 36% and 4 doses by 21%. Should stage 1–2 patient receive adjuvant immunotherapy, 87 percent said yes.

Chemotherapy

Chemotherapy was only used in 35% of cases, of which carboplatin was most popular. Seventy-six percent gives 4–6 doses of carboplatin if used.

Other Questions

If you would find an oral mass during a dental procedure would you proceed with the dental procedure after biopsy of the mass, was answered in the positive by 50% of the audience.

Concerning tongue amputations: The amount of tongue you can amputate in dogs with still have the ability to eat was answered as follows:

Discussion

A major disclaimer of this study was that the study population was extremely skewed towards a surgical oncology attendee at the VSSO symposium, so all data interpretation should be interpreted with caution. In general, the results were very similar to the pre-event enquiry done by 88 VSSO members (data not shown).

As general guidelines for COMM one could extrapolate

• Distant metastases and lymph node involvement are the most important prognostic determinants
• Most people aspirate at least one lymph node before surgery routinely and also remove the ipsilateral lymph node during surgery
• CT of the chest is the preferred technique for thoracic and abdominal ultrasound for evaluation of the presence of metastases.
• COMM should be excised with wide or radical margins and marginal cuts should be redone.
• The role of chemo- or radiation therapy is unclear at the moment, radiation therapy is most commonly used for tumors that cannot be cut and of the chemotherapy options, at least 4 doses of carboplatin is the most used.
• The MM vaccine is used often by this audience, also for stage 1–2 patients, but not everyone is convinced of its efficacy. At least 4 doses are preferred.
• There are strict differences between dogs and cats of how much tongue you can remove without affecting the ability to eat or drink.

References

1.  Smith SH, Goldschmidt MH, McManus PM. A comparative review of melanocytic neoplasms. Vet Pathol. 2002;39:651–678.

2.  Bergman PJ. Canine oral melanoma. Clin Tech Small Anim Pract. 2007;22:55–60.

3.  Modiano JF, Ritt MG, Wojcieszyn J. The molecular basis of canine melanoma: pathogenesis and trends in diagnosis and therapy. J Vet Intern Med. 1999;13:163–174.

4.  Manley CA, et al. Xenogeneic murine tyrosinase DNA vaccine for malignant melanoma of the digit of dogs. J Vet lntern Med. 2011;25:94–99.

5.  Bergman PJ, et al. Long-term survival of dogs with advanced malignant melanoma after DNA vaccination with xenogeneic human tyrosinase: a phase I trial. Clin Cancer Res. 2003;9:1284–1290.