A melanoma is a type of cancer that originates from pigment producing cells called melanocytes

Melanomas in the oral cavity or toenail bed have a high metastatic rate

Surgery is an important treatment for this type of cancer, however, other treatments such as the melanoma vaccination, chemotherapy and radiation may also be needed

What is it?

• A melanoma is a type of cancer that can develop in
  • the skin
  • toe nail bed
  • lips
  • eye
  • intestine
  • other unusual places
• They originate from the pigment-producing cells called melanocytes; skin tanning is due to pigment production by melanocytes
• If these tumors are located on the haired skin (except the toenail bed) they usually do not metastasize
• Digital (toe) melanomas
  • Of all digital tumors, 17.3% have been reported to be melanomas
  • These tumors have a very high spread rate; one third of these have spread to the lungs at the time of diagnosis
• Oral (mouth) melanomas
  • is locally invasive and metastasizes rapidly to the regional lymph nodes and lungs.
  • a subgroup of melanomas on the lips and oral cavity have a very low tendency to metastasize and aggressive surgery commonly is curative
    

Signs

• Signs that an owner may see
  • black or brown lump
  • pink lump is seen if the melanoma dose not produce pigment
  • Signs of an oral melanoma ma include drooling, bad breath, reluctance to chew hard food, blood coming from the mouth and a black or pink mass in the mouth
  • Signs of a digital melanoma may cause the toe to swell and may cause lameness. Initially, this tumor of the digit may resemble an infection of the toe; however, treatment with antibiotics does not resolve the swelling.
• Signs that a veterinarian may see
  • enlargement of lymph nodes in the area of the tumor
• Signs of spread of the tumor to the lungs
  • there may be no signs at the time of evaluation if early spread of the tumor is present
  • breathing difficulty, coughing, weight loss, poor appetite and malaise

Diagnosis

• Fine needle biopsy - usually does not require anesthesia or sedation unless the tumor is deep within the mouth
• Core biopsy - requires anesthesia of some sort - local or general
• 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 and abdominal ultrasound - to help rule out spread of cancer to the lungs and internal organs
• Lymph nodes in the area of the tumor are evaluated with a fine needle biopsy to rule out spread of the cancer. In some cases the oncologist or surgeon may also recommend removal of local lymph nodes to check for spread of cancer
  

Treatment

• Surgery is an essential in most cases
  • Amputation of the toe if the tumor is located on the toenail bed
  • Tumors located in the oral cavity require an aggressive surgery (mandibulectomy or maxillectomy) to remove all local disease
  • Tumors located in the haired skin (except for the nail bed) typically are benign and only require conservative surgery
• Chemotherapy
  • In some cases our oncologist may recommend chemotherapy which entails administration of one treatment every 3 weeks for a total of 4 to 6 treatments; most patients tolerate the chemotherapy medication with mild or no side effects
• Radiation therapy
  • is used to treat a tumor if it is inoperable or if the surgery did not removal all of the tumor
  • 18 to 21 radiation treatments are administered to the tumor site and regional lymph nodes, starting 2 weeks after the tumor has been removed
• Melanoma vaccine
  • this is a new treatment that requires administration of a series of inoculations, can help the body to kill residual tumor cells; best results are achieved when all visible tumor has been removed

Homecare

• Analgesics to control pain after surgery
• Check the incision daily for infection - especially for the first 2 weeks after surgery
• Restrict exercise for 3 weeks or more if indicated by the surgeon
• Melanoma vaccination should be started as soon as a diagnosis of melanoma has been established
• Radiation and/or chemotherapy can start 2 weeks after surgery

Prognosis

• Oral melanomas
  • the larger the tumor the worse the prognosis
  • 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
  • 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
  • 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
    • mitotic index on the biopsy report
  • Radiation therapy has been reported to have excellent local control of oral melanomas; it does not prevent or treat metastasis of the tumor to the lungs and other distant sites; radiation 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. 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
• Skin melanomas
  • have a high cure rate with simple surgical removal

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. 2009 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.