Surgery is the most effective local treatment for melanomas. Small tumors (<2 cm in diameter) that are not attached to the underlying tissue layers, are well defined and grow slowly and are generally benign, allowing the dog to heal completely through surgery. Large, ill-defined, rapidly growing tumors (> 2 cm) with ulceration are difficult to remove completely by surgery.
Because melanomas are so invasive and can spread quickly, wide margins need to be calculated when the tumor is removed. With melanomas that occur on the gums, it is possible that this involves the removal of part of the upper or lower jaw. With melanomas in the cheeks, lips or tongue, bone removal is often not necessary. In general, a margin of 1 to 3 cm should be calculated depending on the degree of the tumor (ideally 1 layer of tissue). If only incomplete margins (space around the tumor) can be obtained, the combination of surgery with radiotherapy or additional treatments such as chemotherapy and immunotherapy is recommended.
Melanomas are considered relatively insensitive to radiation therapy (although much depends on the radiation therapy protocol). However, radiation therapy is considered an effective therapy for the local control of oral melanoma with minimal side effects in dogs. Usually, the tumor of the oral cavity and the local lymph nodes (mandibular and retropharyngeal) are treated. Typically, a margin of 2 cm is applied around the tumor or the surgical incision site.
- Curative radiotherapy (with healing intent):
- Malignant melanomas generally respond well to dose fractionation (with a total of 6 fractions either 1x / week for 6 weeks or 2x / week for 3 weeks).
Response to treatment occurs fairly quickly (tumor size decreases within weeks of first treatment).
Relapse: Depends on the protocol used. When cancer cells are still microscopically present, 26% of the treated dogs relapse. When macroscopic cancer tissue is still present, 45% of the treated dogs relapse. In tumors smaller than 5 cm3, the chance of a cure via radiotherapy is more likely.
A complete or partial reduction of the tumor usually occurs after radiation, although it is often temporary. Average survival time: 5.3-11.9 months.
De prognose verbetert naarmate de tumor meer vooraan in de mond gelegen is, er geen radiografisch bewijs is van botaantasting en geen microscopisch detecteerbare kankercellen aanwezig zijn.
The prognosis improves as the tumor is located more at the front of the mouth, there is no radiographic evidence of bone damage and no microscopically detectable cancer cells are present.
The side effects of radiotherapy depend on various factors such as the total dose used, the dose / fraction and the volume of tissue in the irradiation field.
Rapidly occurring side effects can include swelling of the mucous membranes, as well as mild inflammation with possible pain, bleeding, ulceration and tissue death of the gums, tongue and cheek mucosa. At the level of the skin, the skin may feel dry and a skin thickening and baldness may occur in that place. These side effects usually recover within 1-2 weeks of treatment. Side effects can also occur at a later time: in 1/10 dogs a certain amount of bone tissue death has been observed in the long term and tumors can also paradoxically develop through radiation.
- Palliative radiotherapy:
- This is a form of radiotherapy that is not intended to cure, but to slow down the disease. This form of treatment is mainly used in metastatic or advanced oral malignant melanoma.
Chemotherapy may be appropriate in dogs with malignant melanoma because of the high risk of metastasis (up to 75%). This chemotherapy can be administered directly into the tumor or intravenously. Until now, chemotherapy has not been shown to be very effective in melanomas.
- Intralesional chemotherapy (directly in the tumor):
- The information about these treatment options is rather anecdotal. Implants that release the chemotherapeutic agent cisplatin are placed in the tumor. With this treatment, up to 70% of treated dogs may experience temporary tumor reduction, but no cure. One can also inject cisplatin into the tumor and then apply electrodes to the tumor. These provide a small shock that temporarily causes pores in the cancer cells. Through these pores, the chemotherapeutic agent penetrates into the cancer cells which die. The latter treatment is not yet standard treatment in veterinary medicine and cannot be offered on a regular basis due to the need for a special device called an electroporator.
- Systemic chemotherapy:
- The best clinical effects against oral malignant melanomas have so far been obtained with chemotherapeutics such as carboplatin and cisplatin.
Immunotherapy is a promising additional treatment for dogs with oral malignant melanomas. Until recently, the most popular supportive / adjunct treatment was chemotherapy. However, melanomas are not very sensitive to chemotherapy, which means that immunotherapy is gradually becoming more and more prominent as an alternative method to stop the division of cancer cells.
At the moment, there are not many immunotherapeutic treatments in circulation in Belgium or the Netherlands.
- is a therapeutic cancer vaccine that produces a protein (tyrosinase), which is a protein specific for melanocytes (pigment cells). This vaccine teaches the dog's body to better recognize and keep the cancer cells in check. This treatment is especially indicated for the treatment of dogs with stage II or III oral melanoma and in whom (after treatment) tumor growth could be stopped. The results of this vaccine were compared with data obtained in the past for dogs with this tumor type. This comparison showed that the survival time doubled after the administration of the cancer vaccine.
For example, stage I-III melanomas that were locally controlled had an average survival time of 1075 days, while stage I-III melanomas that were not locally controlled had an average survival time of 553 days. However, caution should be exercised when interpreting these results because, due to increasingly early detection, better treatment methods and methods dogs have a longer survival today than in the past. This vaccine would be especially interesting as an additional treatment when as little cancer tissue as possible is present (eg after surgery).
- Pet Biocell
- is a German company that makes cancer vaccines. To date, there are not enough large studies available to show that this treatment works.
- Elias Animal Health
- is an American company that makes cancer vaccines and collects white blood cells after administration. When the white blood cells that specifically recognize the cancer cells are cultured in large numbers, they are returned to the dog to more efficiently kill the cancer cells. For the time being, only results for a bone tumor are known.