Key Points

Melanomas located in the mouth, lips and toenail bed usually are very malignant

Melanomas located in haired skin generally are benign

A combination of surgery and adjunctive therapy such as melanoma vaccination, radiation and/or chemotherapy may be recommended

Prognosis for malignant melanomas is guarded, but newer treatments are giving hope for long-term survival

 

Melanomas

Melanoma is a tumor that can develop in the skin, toe nail bed, lips, eye, intestine and other unusual places. These tumors originate from the pigment-producing cells called melanocytes. These cells are responsible for giving humans a tan with sun exposure. Melanomas located on the haired skin (except the toenail bed) generally usually do not spread to other organs. Of all digital tumors, 17.3% have been reported to be melanomas. These tumors have a very high spread rate. At the time of diagnosis of a digital melanoma, roughly one-third of dogs will have detectable of the tumor spread to the lungs. Melanoma is the most common oral tumor. This tumor is locally invasive and spreads rapidly to the regional lymph nodes and lungs. Certain types of melanomas on the lips and oral cavity have a very low tendency to spread and have a very good chance to be cured with surgery.

 

Signs

A brown or black mass (lump) is the most common sign of a melanoma. Some melanomas are not pigmented and may appear as a pink mass. A melanoma in the oral cavity may produce signs of drooling, bad breath, reluctance to chew hard food, blood coming from the mouth and a black or pink mass in the mouth. A melanoma that involves the toenail bed may cause the toe to swell and may cause lameness. Initially, this tumor of the digit may mimic the appearance of an infected toe; however, treatment with antibiotics does not resolve the problem. Enlargement of lymph nodes in the area of the tumor may be a sign of spread of the tumor to these nodes. If the patient has spread of tumor to the lungs, potential clinical signs may include breathing difficulty, coughing, weight loss, poor appetite and malaise.

 

Diagnosis

The diagnosis of a melanoma is based upon a fine needle biopsy or surgically collecting a piece of tissue from the mass. If the fine needle biopsy does not provide a definitive diagnosis, a core of tissue may be required. A complete blood count, chemistry profile and urine testing are done to evaluate the health status of your companion’s internal organs prior to anesthesia and surgery. Chest x-rays are used to help rule out spread of cancer to the lungs and lymph nodes in the chest. Abdominal ultrasound is also performed to rule out spread of tumor to the internal abdominal organs. Lymph nodes in the area of the tumor are evaluated with a fine needle biopsy to rule out spread of the cancer. If this test does not provide a clear-cut answer, removal and microscopic analysis of a regional lymph node is recommended.

 

The day of surgery

Our anesthesia and surgical team will prescribe a pain management program, both during and after surgery that will keep your companion comfortable. This will include a combination of general anesthesia, injectable analgesics, local anesthetics, oral analgesics and anti-inflammatory medication. The surgeon will call you with an update after surgery.

 

Treatment

Surgery is an essential treatment for a melanoma. If the tumor is located on the toenail bed, amputation of the entire toe is essential. Tumors located in the oral cavity require an aggressive surgery to remove all local disease. Commonly, these tumors invade into the bone; therefore, a portion of the jawbone must be removed with the tumor to achieve local control of the disease. Melanomas located in the haired skin (except for the nail bed) typically are benign and only require conservative simple surgical removal. In certain cases, an oncologist may recommend chemotherapy for melanomas. Typically, one treatment is performed every 3 weeks for a total of 4 to 6 treatments. Most patients tolerate the chemotherapy medication with transient mild side effects. Radiation therapy has been shown to prevent or delay the onset of tumor regrowth. Eighteen to 21 radiation treatments are administered to the tumor site and regional lymph nodes, starting 2 weeks after the tumor has been removed. Radiation treatments are administered Monday through Friday with no treatment during weekends. A short anesthesia is required to administer each radiation treatment. A melanoma vaccine, which requires administration of a series of injections, can help the body to kill residual tumor cells. Best results are achieved when all visible tumor has been removed.

 

Aftercare

After surgery, a prescribed pain reliever should be given to minimize discomfort. It’s also extremely important to limit your companion’s activity and exercise level for three weeks after surgery. The incision should be checked daily for signs of infection. Two weeks after surgery, the surgeon will monitor the healing process and our oncologist will initiate adjunctive therapy (melanoma vaccination, chemotherapy or radiation therapy), if indicated by the biopsy report.

 

Results

Oral melanomas: The size of a melanoma and stage of the disease (presence of metastasis) directly affects the survival time. Patients with stage 1 tumors (less than a 2 cm diameter mass and no metastatic disease) that are surgically removed have medial survival times of 17 to 18 months. Patients with stage II tumors (2 cm but less than 4 cm in diameter mass with no metastasis) that are surgically removed have median survival times of 5 to 6 months. Patients with stage III tumors (4 cm and larger mass with spread to regional lymph nodes) have median survival times of 3 months. Stage IV tumors are those that have already spread to distant sites such as the lungs and survival times are weeks to a few months.

Negative prognostic factors include advanced stage of the disease, evidence of metastasis and the mitotic index on the biopsy report. Death of the patient is usually due to metastatic disease (spread of tumor) typically to the lungs.

Radiation therapy has been reported to have excellent local control of oral melanomas, yet does not prevent or treat the spread of the tumor to the lungs and other distant sites. Therefore, this modality should be used in conjunction with the melanoma vaccine for improved survival times.

Vaccination with the melanoma vaccine reportedly gave excellent long-term control of the disease and survival times. Bergman reported only minimal to no side effects, which at worst was mild local reaction at the injection site. The best result was seen with intradermal vaccination that must be administered with a special injector system. Currently, their published data was limited to 9 dogs treated with surgery and melanoma vaccine in dogs in which one dog with stage IV disease had complete resolution of tumors in the lungs for 329 days. Two dogs that had stage IV disease had survival times of 421 and greater than 588 days. Two dogs that had stage II/III disease had survival times of 501 and 496 days. Four of nine dogs had no positive response to the vaccine. Digital melanomas: Digital melanomas treated with surgical amputation of the digit resulted in a median survival time of 365 days. Digital melanomas that are not located on the nail bed and have benign characteristics (low mitotic index) can be potentially cured with surgery alone. Skin melanomas: Melanomas that are located in the skin (except for the nail bed) carry an excellent prognosis with simple surgical removal or digit amputation, as they have a very low spread rate.

 

References

1. Esplin DG. Survival of dogs following surgical excision of histologically well-differentiated melanocytic neoplasms of the mucous membranes of the lips and oral cavity. Vet Pathol. 2008 Nov;45(6):889-96.
2. Bergman PJ, et al. Development of xenogeneic DNA vaccine program for canine malignant melanoma at the Animal Medical Center. Vaccine. 2006 May 22;24(21):4582-5.
3. Bergman PJ, et al. Long-term survival of dogs with advanced malignant melanoma after DNA vaccination with xenogenic human tyrosinase: a phase 1 trail. Clin Cancer Res 2003 Apr; 9(4):1284-90.
4. Bergman PJ. Canine oral melanoma. Clin Tech Small Anim Pract. 2007 May;22(2):55-60.
5. Wobeser BK, et al. Diagnoses and clinical outcomes associated with surgically amputated canine digits submitted to multiple veterinary diagnostic laboratories. Vet Pathol. 2007 May;44(3):355-61.
6. Williams LE, et al. Association between lymph node size and metastasis in dogs with oral malignant melanoma: 100 cases (1987-2001). J Am Vet Med Assoc. 2003 May 1;222(9):1234-6.
7. Blackwood L, et al. Radiotherapy of oral malignant melanomas in dogs. J Am Vet Med Assoc. 1009 Jul 1:209(1):98-102.
8. Marino DJ, et al. Evaluation of dogs with digit masses: 117 cases (1981 -1991). J Am Vet Med Assoc. 1995 Sep 15;207(6):726-8.