Issue Description Melanoma is a type of cancer that occurs
commonly in dogs with pigmented (dark) skin. Melanomas can occur in
areas of haired skin, where they usually form small, dark (brown to
black) lumps, but can also appear as large, flat, wrinkled masses.
Melanomas also can occur in the mouth, toes, or behind the eye. In
general, skin melanomas tend to be benign, and those in the mouth,
toes, or eyes tend to be malignant. Other Names Canine Melanoma
Causes Melanoma arises from melanocytes, cells that
impart pigment or coloration to the skin. In humans, melanoma arises
due to mutations induced by repeated, intense exposure to ultraviolet
light (for example, frequent tanning or working outdoors). This does
not seem to be a major factor in dogs, as in most breeds the hair coat
affords them protection from sunlight. However, pigment cells divide
every time there is injury to the skin, or if there is constant trauma
(for example, areas where dogs constantly scratch or lick).
Nevertheless, risk factors for Melanoma are not well
Mutations that contribute to cancer can also
be inherited. An inherited mutation in a single gene that is important
in cell growth control will increase the risk of that individual to
develop cancer. This can be due to reducing the overall number of
acquired mutations that must accumulate before a cell becomes
cancerous, or it can be due to disabling a critical safeguard gene
that normally prevents cells from becoming tumors. Specific genes that
are responsible for familial melanoma have been identified in humans
and in mice. In dogs, there appears to be a predisposition among
certain breeds or families to develop specific types of cancer,
suggesting that a hereditary component may be important in the
development or progression of the disease.
Common Symptoms Of Cancer
Hesitation to exercise or loss of energy.
Loss of appetite, weight loss.
Persistent lameness or stiffness of movement.
Lumps in the breast area.
Abnormality or difference in size of testicles.
Abnormal swellings that continue to grow, especially in the nymph
Sores do not heal.
Bleeding or discharge from the mouth, nose, urinary tract, rectum,
Difficulty eating or swallowing.
Difficulty in urinating or defecating.
Diagnosis A physical exam, blood tests, a chest x-ray and
a biopsy when the veterinarian believes it is necessary.
Treatment Treatment of melanoma includes surgery,
chemotherapy and radiation. Surgery will be performed to remove as
much of the tumor as possible. Chemotherapy is used including
Dacarbazine. Radiation is used as a treatment because it aides in the
shrinking of the tumor.
Prognosis The prognosis for Melanoma is poor at
best when found in the dog's skin. The prognosis for Melanoma
is even poorer when it is located in the mouth, toes or behind the
eyes. Tumors spread quickly when they are not treated and they may
spread even if treatment is tried. Melanoma may even reoccur