|The most common location for oral melanoma is the gum (gingiva) or the buccal mucosa (inside of the cheek) but other
locations have been reported such as the inner lining of the lips, palate and tongue. Oral melanomas are locally
aggressive and also have a high likelihood (80%) of metastasis (spread) to other organs such as the regional lymph nodes
and lungs. Although most oral melanomas are very aggressive, there may be a small subset of these tumors, possibly
including lingual (tongue) melanomas, that may be less metastatic.
What are the symptoms of oral melanomas in cats and dogs?
Most cats and dogs with oral cancer have a mass in the mouth noticed by the owner. Pets with oral tumors will typically
have symptoms of increased salivation (drooling), facial swelling, mouth bleed, weight loss, foul breath, oral discharge,
difficulty swallowing, or pain when opening the mouth. Loose teeth could be indicative of bone destruction due to the tumor.
How is the diagnosis made?
A thorough diagnostic evaluation of oral tumors is critical due to the variety of different tumors that could be present.
Sedation or anesthesia is often required in order to examine the pet's mouth, especially if the suspected tumors are
located in the back of the mouth or on the tongue. If the tumor is suspected to be malignant, chest X-ray can be done prior
to biopsy to check for metastasis (spread) to the lungs. Bone destruction is not typically seen on X-rays of the mouth until
>40% of the bone is destroyed so what appears to be a normal X-ray cannot exclude the tumor's bone invasion. Advanced
imaging such as CT (computed tomography) or MRI (magnetic resonance imaging) can be valuable tools in staging the
disease (determining how advanced it is), especially for evaluating bone invasion and tumor's potential extension into the
nasal cavity, pharynx or the eye. The use of CT may eliminate the need for regular X-rays but CT/MRI imaging is more
Regional lymph nodes should be carefully assessed for any abnormalities, although lymph node size is not an accurate
predictor of metastasis. In a study of 100 dogs, 40% showed normal sized lymph nodes despite being positive for cancer
cells, and 49% of dogs who showed lymph node enlargement did not actually have lymph node metastasis. Lymph node
aspirates (isolation of cells for microscopic analysis to check for the presence of any cancer cells) are, therefore,
recommended for pets with oral cancers.
The final diagnostic step, which is done under anesthesia, is a large incisional biopsy. Biopsy is preferred over cytology to
definitively differentiate between benign (noncancerous) and malignant (cancerous) tumors and determine the exact type
of the tumor present. This is important in order to plan treatment that will best maximize the pet's response and survival.
Do tumors cause pain in cats and dogs?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or
injury. It is, therefore, essential that veterinary teams that are taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets. The best way to manage cancer pain in pets is to
prevent it, a term referred to as preemptive pain management. This strategy anticipates pain ahead of time and
administers pain medication before the pet actually experiences pain, thus ensuring the pet's maximum comfort.
To learn more about how to recognize pain in pets with cancer and what cancer pain management options are available for
your pet, please visit the Cancer Pain Management section.
How important is nutrition for pets with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).
Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the Nutrition for Pets with Cancer section.
What are the treatment options for oral melanomas?
Surgical removal of oral melanoma is the primary method of treatment whenever possible. Since many oral melanomas
invade the bone, the surgery will aim to remove not only the tumor itself but also any associated bone structures. For oral
melanomas, an aggressive surgery is usually recommended given the aggressive nature of these tumors. Cosmetic
appearance is generally good after most upper or lower jaw surgeries but can be challenging when both sides have to be
surgically treated. For an overview of the surgical treatment of oral cancers as well as possible post-surgery complications,
please click here. While surgery can reduce the risk of local recurrence (tumor coming back), unfortunately, most dogs will
eventually succumb to the tumor's spread to other organs. In a published study of 37 dogs whose oral melanomas in the
lower jaw were removed by partial mandibulectomies (surgery where part of the lower jaw was removed), median survival
time was 9.9 months (range 1-36 months), and 21% of dogs were alive after one year. Twenty of the 37 dogs were
euthanized due to recurrent or metastatic disease (Kosovsky, Vet Surg, 1991).
Radiation therapy can be used in a variety of settings. It can be used as a primary treatment for oral tumors that cannot be
removed surgically or in combination with surgery for tumors that were not completely removed with surgery. There is some
evidence that radiation therapy may be beneficial for dogs with oral melanoma, although optimized radiation protocols still
need to be developed. In a retrospective analysis of 140 dogs with oral melanoma treated with three different radiation
protocols, the median survival time was 7 months. The study identified certain risk factors that affected the outcome of
dogs with oral melanomas such as the location of the tumor (back vs front), tumor size (small vs large), and whether the
bone was affected (lysed vs non-lysed). Dogs without any risk factors (front location, small size and no bone lysis) had
median survival time of 21 months. In contrast, dogs with one of these risk factors (back location or large size or bone lysis)
had median survival time of 11 months, dogs with two risk factors had median survival time of 5 months, and dogs with
three risk factors had median survival time of only 3 months. Although three different protocols of radiation therapy were
used in this study, there was no difference between them in terms of outcome (Proulx, Vet Radiol Ultrasound, 2003).
In general, chemotherapy tends to produce only very modest response in dogs with oral melanoma. Chemotherapy may be
offered when pet owners decline surgery and/or radiation therapy. In dogs, commonly used chemotherapy drugs are
platinum-based such as carboplatin or cisplatin. In a small study that evaluated cisplatin in combination with another drug
called piroxicam in 11 dogs with oral melanomas, two dogs achieved compete response. The most commonly observed
toxicity associated with this regimen was cisplatin-induced kidney toxicity (Boria, J Am Vet Med Assoc, 2004).
The efficacy of combining carboplatin with radiation therapy is still somewhat unclear. In one retrospective study of 39 dogs
(Stage I oral melanoma incompletely removed by surgery) who were treated with carboplatin or cisplatin plus radiation
therapy, 15% experienced local recurrence (tumor coming back) within median time of 139 days, 51% of dogs developed
metastases in other organs within median time of 311 days, and median survival time was 363 days (Freeman, J Vet Intern
Med, 2003). In another retrospective analysis of 28 dogs with oral melanomas (without lung metastases), there appeared
to be no significant difference in survival between using radiation alone and radiation combined with chemotherapy:
median survival for 13 dogs treated with radiation alone was 307 days compared to 286 days for 15 dogs treated with
radiation plus carboplatin (Hayes, Vet Comp Oncol, 2005).
Vaccine for oral melanomas in dogs
In March 2007, the U.S Department of Agriculture granted a conditional approval of a DNA vaccine against dog melanoma.
This was the first time that the U.S. government approved a therapeutic vaccine for the treatment of cancer in either
animals or humans. The vaccine was developed through a partnership between Merial, Memorial Sloan-Kettering Cancer
Center (MSKCC) and The Animal Medical Center (AMC) of New York. Clinical studies of the vaccine in dogs showed
significantly longer life spans even in dogs with advanced stages of melanoma. The vaccine is administered via a new
Canine Transdermal Device, which delivers the vaccine without the use of a needle. The approved protocol involves
administration of a dose of the vaccine every two weeks for four treatments, followed by a booster dose every six months.
The vaccine received full approval in 2010.
Where do I find a qualified veterinary oncologist?
To locate a qualified veterinary oncologist worldwide who can discuss with you appropriate cancer treatment plan for your
pet's cancer condition, please visit the "Locate a veterinary oncologist" section.
Are there any clinical trials investigating new treatments?
Currently, there are clinical trials investigating new treatments for oral melanoma in dogs. To learn more about these trials
(which are partially or fully funded by the institutions), please visit Melanoma Clinical Trials for Dogs.
To learn more about veterinary clinical trials in general, please visit the Clinical Trials in Cats and Dogs section.
What is the prognosis?
Oral melanoma is an aggressive disease with a high potential to metastasize to other organs, namely the lungs. The
median survival of dogs with no treatment is 65 days. The median survival for dogs treated with surgery alone varies from
150-318 days with less than 35% of dogs surviving one year post-diagnosis. When combined with chemotherapy, the
median survival is modestly improved. The median survival time for dogs treated with radiation therapy is 211-363 days
and for cats 66-224 days. Other factors such as the tumor size, stage and success of the first treatment can also predict
how well or poorly the pet will do. Dogs with tumors smaller than 2cm diameter have a median survival time of 511 days
compared to 164 days for those with tumors greater than 2cm diameter or lymph node metastasis. This is in contrast to
dogs with tumors bigger than 2cm and metastases, who usually succumb to the disease within five months (approximately
25% of dogs will be alive one year after diagnosis if treated).
Additional online sources:
|Oral Melanoma in Cats and Dogs
|PET CANCER CENTER
Comprehensive guide to cancer diagnosis and treatment in cats and dogs