Shelby is an 11 year
old lovely golden retriever who was diagnosed with malignant melanoma of the
digit (toe) in April 2011.
Shelby developed a
broken toe nail on her right front limb.
When the lesion did not respond to conservative treatment, the toe was
removed and sent for biopsy. Results
returned showing malignant melanoma of the tissue surrounding the nail bed.
A lymph node aspirate,
of the right prescapular lymph node, was performed to check for local spread of
the cancer. This lymph node is located just in front of her right shoulder and
would be the next place we might expect her cancer to spread. Luckily for
Shelby, the melanoma had not yet spread to the lymph node. Thoracic radiographs
(x-rays) were also performed to check for spread of the cancer and were
negative for any metastasis.
Malignant melanoma is a
relatively common cancer in dogs that is found more often in the mouth, nail
beds, foot pads and eyes. As in humans, it can appear anywhere on the body, but
ultraviolet exposure (sunlight) has not been proven as a primary cause. This is
because dogs (and cats) have a thick hair coat that appears to protect them
from the sun. Also, not all skin masses diagnosed as melanoma are malignant; in
fact many cutaneous melanomas are benign in dogs.
Shelby met with the
medical oncology department here at VCA Veterinary Referral Associates in early
June 2011. Despite no detected spread of
her cancer, microscopic cancer cells could still be lurking in her body, so
Shelby’s owners chose to start the Oncept® melanoma vaccine right away.
Oncept ® is given once
every other week for 4 injections then boostered once every 6 months. The vaccine
contains human DNA encoding the gene for tyrosinase, which is a protein that
gives pigment to skin cells, and is found in healthy cells but also in melanoma
cells. The dog’s body processes the DNA and actually synthesizes the human
version of tyrosinase, which is “flagged” by its immune system as an invader.
Because human tyrosinase is structurally similar to the dog’s tyrosinase, the
dog’s immune system will attack the tyrosinase protein in the cancerous
melanoma cells, thereby destroying microscopic tumor cells.
Shelby visits every six
months for a physical exam, thoracic radiographs, and a booster melanoma
vaccine. Since her last recheck in January, Shelby is free of any detectable
disease. In her spare time, she works as a model for a greeting card line
designed by her mom!
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