|Oral squamous cell carcinoma (SCC) is the second most common oral tumor in dogs. SCCs are typically classified into two
categories: tonsillar SCC (cancer affecting the tonsils) and non-tonsillar SCC (cancer affecting other structures, such as the
gums and tongue). It is estimated that 50-78% of oral SCCs are non-tonsillar. SCCs in the gum tend to be locally aggressive
and invade the bone, but they are less metastatic in nature (10-20% of cases) compared to oral melanomas. In contrast,
SCCs in the tonsil metastasize early on to regional lymph nodes and other organs such as the lungs, thyroid, spleen, liver,
kidney or bone. SCCs in the tongue usually show behavior somewhere between that of gum and tonsil tumors, with some
tumors spreading to either lymph nodes or other distant organs.
What are the symptoms of oral squamous cell carcinomas in dogs?
Most dogs with oral cancer have a mass in the mouth noticed by the owner. Dogs 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). Bone destruction is not typically seen on X-rays until 40% or more is destroyed and 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 expensive.
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 have metastasis. Lymph node aspirates (isolation of
cells for microscopic analysis to check for the presence of any cancer cells) are 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 or
aspirates to definitively differentiate between benign (noncancerous) and malignant (cancerous) tumors and determine the
exact type of tumor present. This is important in order to plan treatment that will best maximize the pet's response and
Do tumors cause pain in 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
Cancer Nutrition section.
What are the treatment options for dogs with oral SCC?
Surgical removal of non-tonsillar SCC tumors is the primary method of treatment whenever possible. The exact type and
extent of surgery depends on the tumor's size and location. If an aggressive surgery is needed, it may affect the cosmetic
and functional appearance of the pet; however, cosmetic appearance is generally good after most upper or lower jaw
surgeries. For an overview of the surgical treatment of oral cancers as well as possible post-surgery complications, please
In a published study of 24 dogs whose squamous cell carcinoma tumors in the lower jaw were removed by partial
mandibulectomies (surgery where part of the lower jaw was removed), the dogs were able to live without the presence of a
disease for 26 months (range 6-84 months), and 91% of dogs were alive after one year (Kosovsky, Vet Surg, 1991).
Squamous cell carcinomas of the tongue can also be treated with surgery. While pet owners may be concerned about their
dog's quality of life after surgical removal of the tongue, a report on five dogs who had 80-100% of the tongue removed
showed that the dogs could still have good quality of life after a brief period of adjustment (Dvorak, J Am Anim Hosp Assoc,
Because SCC tumors in the tonsils are very aggressive with an increased rate of metastasis, surgery alone is usually not
sufficient. Additionally, because these tumors are so locally invasive, surgery may not even be possible in some dogs. In a
report of three dogs with tonsillar SCC, surgery alone resulted in survival times of only one, nine and 39 days (Todoroff, J Am
Vet Med Assoc, 1979).
Radiation therapy can be used either as a primary treatment for SCC tumors that cannot be removed surgically (or if pet
owners decline surgery) or after surgery if the tumors could not be completely removed. In a study of 39 dogs with non-
tonsillar SCC treated with radiation therapy, the disease did not progress for a period of 36 months. Of these dogs, six had
local tumor recurrence, one dog showed metastasis to the lymph node, and four dogs showed metastases to distant organs.
The size of the tumor affected progression-free survival rates (defined as the time between completing radiation terapy and
either local recurrence, presence of metastases or death): in dogs with tumors <2cm in diameter, 1-year progression-free
survival rate was 89%; in dogs with tumors 2-4cm in diameter, 1-year progression-free survival rate was 83%; and in dogs
with tumors >4cm in diameter, 1-year progression-free survival rate was only 41%. (Theon, J Am Vet Med Assoc, 1997).
In another study of 14 dogs (of whom six had prior surgery), radiation therapy resulted in median disease-free time interval of
12 months and median survival time of 14 months. Age also appeared to influence the outcome for dogs in this study:
median disease-free survival time for dogs <9 years old was 16 months compared to 7 months for dogs >9 years old; median
survival times were 36 months versus 10.5 months, respectively. It is thought that age-related complications could have
contributed to the different outcomes (LaDue-Miller, Vet Radiol Ultrasound,1996).
For dogs with tonsillar SCC the outcomes are worse. In one study of eight dogs treated with radiation therapy, of whom seven
had lymph node metastases that were not surgically removed, the median survival time was only 3.6 months (MacMillan, J Am
Anim Hosp Assoc,1982).
Chemotherapy is used for oral tumors that have a high metastatic potential such as tonsillar squamous cell carcinoma or for
tumors that cannot be removed by surgery. A drug called piroxicam may have some effect against oral squamous cell
carcinoma in dogs, and can be even more effective when combined with other chemotherapy drugs such as cisplatin or
In a published study of 17 dogs with SCC (any location) treated with piroxicam, one dog (with upper jaw SCC) achieved
complete response, two dogs (one with tongue and one with tonsillar SCC) achieved partial response, and additional five
dogs achieved stable disease (the cancer did not improve but it also did not get worse). For those dogs who achieved
complete response, median time to failure (when the tumor came back or metastasized) was 180 days; for dogs who
achieved stable disease, median time to failure was 102 days (Schmidt, J Am Vet Med Assoc, 2001). In a study of nine dogs
with SCC treated with piroxicam plus cisplatin, two experienced complete response and three had partial responses (Boria, J
Am Vet Med Assoc, 2004). In another study of seven dogs with non-tonsillar SCC, treatment with carboplatin plus piroxicam
resulted in five complete responses (71%) and median survival time of 19.2 months (de Vos, Vet Comp Oncol, 2005).
In a study with eleven dogs diagnosed with oral SCC, using Photochlor (HPPH) as the photosensitizer resulted in eight dogs
being without recurrence for at least 17 months after photodynamic treatment. The potential advantage of this method is that
the cosmetic results are much better compared to those achieved with aggressive surgeries (McCaw, Br Jj Cancer, 2000).
However, given the small number of dogs, more studies are needed to better evaluate the efficacy of this method.
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?
Although there are no clinical trials specifically designed to test new treatments for oral squamous cell carcinomas in dogs,
there are several clinical trials available for dogs with any tumor type for which your pet may qualify. To learn more these
trials (which are partially or fully funded by the institutions), please visit the Dog Clinical Trials (any tumor type) section.
To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials section.
What is the prognosis for dogs with oral SCC?
Several factors will determine the prognosis of a dog diagnosed with oral SCC. For example dogs with tonsillar SCC usually
have a poor prognosis, namely because these tumors are highly metastatic. The prognosis of dogs treated for non-tonsil
SCC is better, particularly for those with tumors located in the front of the oral cavity. Different outcomes are also observed
depending on whether a surgery is performed on the lower versus upper jaw. Following mandibulectomy (surgery of the lower
jaw), the median survival of dogs is 19-26 months, local tumor recurrence occurs in ~10% of dogs and 91% of dogs survive
one year. In contrast, following maxillectomy (surgery of the upper jaw), the median survival is 10-19 months, local tumor
recurrence occurs in 29% of dogs and only 57% of dogs survive one year.
Full course radiation therapy, either alone or following incomplete surgical removal of the tumor, has been effective in
treating oral SCC in dogs. The local tumor recurrence rate is 31% and the median survival time for radiation therapy alone is
15-16 months and increases to 34 months when combined with surgery. The size of the tumor also determines the prognosis.
The median survival of dogs whose tumors were less than 2cm in diameter was found to be 68 months compared to 28
months in dogs whose tumors were 2-4cm diameter compared to 8 months for dogs whose tumors were larger than 4cm.
|Oral Squamous Cell Carcinoma in Dogs
|PET CANCER CENTER
Comprehensive guide to cancer diagnosis and treatment in cats and dogs