Veterinary Society of
Surgical Oncology

General Considerations

  • dermal melanoma is common in dogs and accounts for 5%-7% of all canine skin tumors
  • no sex predilection
  • breed predisposition: Scottish Terrier, Airedale Terrier, Boston Terrier, and Cocker Spaniel
  • mean age 9 years
  • sites: face (especially eyelids), trunk, and extremities
  • gross appearance: solitary with variable pigmentation
  • 2 histologic variants reported in dogs: pilar neurocristic melanoma and clear cell melanoma
  • dermal melanomas are usually benign and are well-defined, deeply pigmented, small, and mobile
  • malignant dermal melanomas appear larger (> 2.5 cm) with ulceration, secondary infection, and rapid growth
  • fibrous dermal melanoma is not malignant
  • junctional melanoma and cellular dermal melanoma can undergo malignant transformation
  • metastasis occurs through both the vascular and lymphatic systems

Treatment

  • surgery
  • ± gene therapy, radiation therapy, local hyperthermia, photodynamic therapy, and intralesional cisplatin
  • durable response to course-fraction radiation therapy
  • responses are short-lived for photodynamic therapy, hyperthermia, and intralesional cisplatin
  • chemotherapy is usually ineffective (agents include mitoxantrone, doxorubicin, platinums, and melphalan)

Prognosis

  • excellent prognosis if benign but guarded if malignant characteristics as metastatic rate between 30%-75%
  • 65% of dogs with malignant dermal melanoma are euthanased within 2 years due to local recurrence or metastasis
  • prognostic factors in dogs include breed, tumor size, infiltration into adjacent tissue, mitotic index, Ki-67 count, DNA ploidy, and monoclonal antibody (MAB IBF9) reactivity
  • 75% melanomas in Doberman and Miniature Schnauzer are benign v 85% melanomas in Miniature Poodle are malignant
  • malignant dermal melanomas < 4 cm have a significantly better MST (12 months v 4 months) and 2-year survival rate (46% v 0%) than tumors ≥ 4 cm
  • Ki-67, proliferation marker to assess growth fraction of tumors, has higher predictive value for biologic behaviour of dermal melanomas than histology
  • DNA ploidy can be used to differentiate benign from malignant melanoma but is not prognostic
  • histology does not predict malignant behaviour in cats compared to dogs (ocular melanoma more likely to be malignant and dermal melanoma more likely to be benign)

DERMAL MELANOMA

Well Differentiated

Poorly Differentiated

Mitotic Index per High Power Field

≤ 2

≥ 3

Survival Time

104 weeks

30 weeks

Death Rate

10%

73%

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