Squamous cell carcinoma is most common digital tumor followed by melanoma

Squamous cell carcinomas have a low metastatic potential, whereas the melanomas have a much higher spread rate

Amputation of the toe is needed for digital tumors

The overall prognosis is favorable

What is it?

• The most common tumors of the toes include the squamous cell carcinoma, melanoma, osteosarcoma, hemangiopericytoma, benign soft tissue tumors, and malignant soft tissue tumors
• Squamous cell carcinoma
  • More than 50% of all digital tumors are squamous cell carcinoma.
  • originates from skin cells
  • very locally invasive
  • commonly destructive to the bone
• Melanoma
  • second most common tumor and accounts for 16% of all digital tumors.
  • originate from the pigment-producing cells in the skin called melanocytes
  • nail bed melanomas spread rapidly to other areas of the body
  • at the time of diagnosis of a digital melanoma, detectable spread to the lungs is seen in one-third of all affected dogs

Signs

• Breeds
  • Squamous cell carcinoma is most commonly seen in large breed dogs with black coats. Over-represented breeds include Labrador Retrievers and Standard Poodles.
• Signs that the pet owner may see
  • swelling of the digit - initially it may appear like a toe infection
  • tumor may include appear black with some melanomas
  • loss of toenail
  • lameness
• Additional signs that the veterinarian may note
  • enlargement of lymph nodes that drain the affected toe
• Signs that may be seen if metastasis is present
  • breathing difficulty
  • coughing
  • weight loss
  • poor appetite
  • malaise

Diagnosis

• Fine needle biopsy - involves only collecting a sample of cells with a needle
• Tissue biopsy (wedge or core)
• Complete blood count, chemistry profile, and urine testing are done to evaluate your companion’s internal organs prior to anesthesia and surgery
• X-rays may show destruction of the bone of the digit, especially if the tumor is a squamous cell carcinoma
• Chest x-rays and abdominal ultrasound are used to help rule out spread of the cancer
• Lymph nodes in the area of the tumor are aspirated to rule out spread of the cancer to the nodes; regional lymph nodes may also be removed and analyzed to rule out cancer

Treatment

• Surgery
  • surgical removal of the entire digit if a malignant tumor is present
  • benign tumors of the skin of the digits may be removed without removing the digit
• Adjunctive therapy
  • chemotherapy or radiation) may be indicated for some malignant tumors. U
  • surgery is all that is needed typically for a squamous cell carcinoma
  • melanomas should be treated more aggressively with surgery, melanoma vaccination, chemotherapy and/or radiation
  • chemotherapy - one treatment is administered 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 during administration of each radiation treatment.

Homecare

• Continue administration of prescribed pain-relieving medication
• Keep the bandage on for 5 to 7 days
• Incision - should be checked for signs of infection after the bandage has been removed
• Diet - A low fat diet may be recommended in some patients; however, a regular diet may be tolerated.
• Antibiotics - prescribed after the surgery if bacterial infection is suspected or confirmed by culture results
• Exercise - restricted for about 3 weeks after surgery
• Recheck evaluations
  • 2 weeks after surgery
  • chemotherapy is typically started 2 weeks after surgery
  • melanoma vaccination can be started as soon as the biopsy report has confirmed the diagnosis

Prognosis

• Digital melanomas
  • median survival time of 365 days with amputation of digit alone
  • the melanoma vaccine can provide excellent long-term control of the disease and increased survival time. Minimal to no side effects are seen with the vaccination.
• Squamous cell carcinoma
  • this tumor has a very good chance to be cured with surgery alone

Complications

• Opening of the incision before it has healed
• Infection
• Tumor recurrence
• Spread of cancer to other parts of the body
• Ongoing lameness following amputation of the digit (rare)
  

References

1. Henry CJ, et al. Canine digital tumors: a veterinary cooperative oncology group retrospective study of 64 dogs. J Vet Intern Med. 2005 Sept-Oct;19(5):720-4.

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. 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.

5. O’Brien MG, et al. Treatment by digital amputation of subungual squamous cell carcinoma in dogs: 21 cases (1987 - 1988). J Am Vet Med Assoc. 1992 Sep1;201(5):759-61.