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Melanoma

Philip J. Bergman, DVM, PhD, DACVIM (Oncology)

Katonah‐Bedford Veterinary Center, Bedford, Hills, NY, USA

Etiology/Pathophysiology/ Signalment
Epidemiology
The most common oral malignancy in the dog is mela-
Melanoma is a relatively common tumor of dogs, espe- noma. Oral malignant melanoma is most commonly
cially in those with significant levels of skin pigmenta- diagnosed in Scottish terriers, golden retrievers, poo-
tion. Melanomas in cats are relatively rare. The most dles, and dachshunds. Oral melanoma is primarily a dis-
common location for canine melanoma is the haired ease of older dogs without gender predilection, but may
skin, where they grossly appear to be small brown to be seen in younger dogs. Additional oral tumor differen-
black masses, but can also appear as large, flat, and/or tials include squamous cell carcinoma, fibrosarcoma,
wrinkled masses. Primary melanomas also can occur in epulides/odontogenic tumors, osteosarcoma, and oth-
the oral cavity, nailbed, footpad, eye, gastrointestinal ers. Melanomas in the oral cavities of dogs are found in
tract, or mucocutaneous junction. Ocular melanomas of the following locations in order of decreasing frequency:
dogs and cats represent a distinct clinical syndrome and gingiva, lips, tongue, and hard palate. Feline melanoma is
will be discussed elsewhere. Metastatic sites for canine relatively rare, but appears to be malignant in most cases.
malignant melanoma (CMM) can be varied, including
local draining lymph nodes, the lungs, liver, meninges,
adrenals, etc. Diagnosis/Pathology/Molecular
Melanoma arises from melanocytes, the cells which Biology
generate pigment through the melanosome by a number
of melanosomal glycoproteins. In humans, cutaneous Melanomas can be difficult to diagnose pathologically in
melanoma can arise due to mutations induced by some situations, especially anaplastic amelanotic mela-
repeated, intense exposure to ultraviolet light (for exam- nomas which can masquerade as soft tissue sarcomas.
ple, frequent tanning or working outdoors). Melanoma is Numerous investigators have attempted to increase the
currently the most rapidly increasing incident human precision of identification of melanomas predominantly
cancer. Significant recent research into the etiology of through immunohistochemical (IHC) means. This may
human melanoma suggests multiple causes which are be accomplished through the use of multiple IHC assays
independent of the aforementioned UV‐associated on suspected melanoma tissue or through the use of an
mutagenesis. Since most breeds of dogs have a hair coat, IHC cocktail of antibodies. The use of PNL2 and tyrosi-
which affords them protection from sunlight, UV‐asso- nase, beyond the typical use of Melan A and S100,
ciated melanoma is a less likely primary causative agent appears to hold particular promise.
in the dog. However, pigment cells divide every time The molecular characterization of canine and feline
there is injury to the skin, or if there is constant melanomas is not as well defined as it is in humans.
trauma (for example, areas where dogs scratch or lick). BRAF is a member of the MAPK signaling pathway,
Nevertheless, risk factors for canine melanoma are not which is commonly mutated in human cutaneous
well established. melanoma, but infrequently mutated in oral mucosal

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical