These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout "What is Cancer". Your veterinarian may suggest certain tests to help confirm or eliminate diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However, information and understanding about tumors and their treatment in animals is improving all the time.
We understand that this can be a very worrying time. If you have any questions please do not hesitate to ask us.
What are squamous cell carcinomas?
"Squamous cell carcinomasare malignant cancers originating from the lining cells of the mouth."
Squamous cell carcinomas are malignant cancers originating from the lining cells of the mouth. They are locally invasive and often recurrent. Only 5-10% of tumors arising in the gums (gingiva) metastasize (spread), but cancers in the tongue often metastasize to local lymph nodes. Cancers that originate from the tonsil metastasize quickly to the other tonsil, lymph nodes of the throat and other parts of the body.
What do we know about the cause?
The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often the culmination of a series of circumstances that come together for the unfortunate individual.
Cancer is essentially the result of non-lethal genetic damage to cells with "external" contributory factors that may be chemical, physical and/or traumatic. The mutated cells upset the normal regulation of cell death and replacement. They do this by activating growth-promoting oncogenes (cancer genes), inactivating suppressor genes and altering the genes that regulate normal, programmed cell death (apoptosis).
"Tonsillar tumors are more common in large cities but rare in rural areas suggesting environmental chemicals may cause some of these tumors."
Papilloma ("wart") viruses may be implicated in some of these tumors. The role of other viruses in cats is uncertain. Tonsillar tumors are more common in large cities but rare in rural areas suggesting environmental chemicals may cause some of these tumors. In people, it is suggested that as many as seven genetic 'hits' (episodes of gene damage) are required to induce full cancerous growth, a process that takes approximately five years.
Why has my pet developed this cancer?
Some animals have a greater tendency (genetic susceptibility) to cancer and some breeds develop far more of these cancers than others. In some cases, your pet may have been infected with species-specific papilloma viruses or have had contact with everyday environmental chemicals that can induce or promote cancer.
Are squamous cell carcinomas common?
The gingival tumors are common and occur in adult dogs and cats without breed or sex predilection. Dogs are usually middle-aged, and tend to be slightly younger than those developing other types of malignant oral tumors. Large dogs are more likely to have tumors and male dogs, particularly German Shepherd dogs, have the highest prevalence of tonsillar tumors. Oral tumors are common in cats. Ten percent of all feline neoplasms occur in the mouth and of these almost 90% are malignant. Seventy-five percent of oral tumors are squamous cell carcinomas.
How will this cancer affect my pet?
These tumors are usually noticed as swellings, which frequently ulcerate and bleed, and may become secondarily infected, causing bad breath. Other common clinical signs include drooling saliva, difficulty in eating, displacement or loss of teeth and facial swelling.
"You may observe one or more of these clinical signs before you notice lumps in the tongue or tonsils."
You may observe one or more of these clinical signs before you notice lumps in the tongue or tonsils. There may be pain and swelling of the local lymph nodes. Tumors in the back of the throat (pharynx) are particularly painful and cause difficulty with swallowing. A few tumors induce signs, called 'paraneoplastic syndromes', which are not readily explained by local or distal spread of the tumors. In cats, abnormal hormone production by some cancers has induced increased blood calcium levels.
How is this cancer diagnosed?
Clinically, oral tumors often have a typical appearance. The growth rate of oral tumors is a very important diagnostic factor. X-rays may be useful to detect whether tumors have invaded the bones and to guide surgery. Loss of bone adjacent to the tumor usually means a poorer outlook (prognosis) because malignant gum tumors destroy bone whereas benign ones tend to make the adjacent bone grow.
"Malignant gum tumors destroy bone whereas benign ones tend to make the adjacent bone grow."
Accurate diagnosis of these tumors requires microscopic examination of tumor tissue. Cytology, the microscopic examination of small samples of cells, rarely helps in the diagnosis of these tumors. Definitive diagnosis, prediction of behavior (prognosis) and an assessment of the completeness of removal rely on microscopic examination of tissue (histopathology). Histopathology also rules out other cancers. Your veterinarian will submit either a small part of the mass (biopsy) or the whole lump to a specialized laboratory, where a veterinary pathologist will examine and diagnose the lesion. If your veterinarian submits the entire mass, the pathologist may be able to indicate whether the cancer has been completely removed.
Most squamous cell carcinomas invade the bone of the jaw. For complete removal, these need wide surgical margins, usually including substantial parts of the jawbone. Tissue samples that contain bone will need decalcifying, so it may take a few weeks before the final histopathology results are available.
What types of treatment are available?
Surgical removal is the standard method of treatment for all oral tumors. The invasive cancers are difficult to remove completely so large pieces of the jawbone may be removed (hemimaxillectomy or hemimandibulectomy). If your pet requires one of these complex and extensive surgeries, your veterinarian may refer you to a specialist at a veterinary referral center.
Surgery combined with post-operative radiotherapy is considered the best treatment in people, but radiotherapy sometimes needs to be given every eight hours and is only available for animals at a few referral centers. Chemotherapy does not improve survival. Photodynamic therapy is used for superficial tumors in people but is not yet available in animals and most tumors are too deep at presentation for this treatment.
These tumors provoke an inflammatory reaction that causes pain, and reducing inflammation can bring some clinical relief. Tumors of the tonsils and throat are painful and the pet requires pain control medication.
Can this cancer disappear without treatment?
"Treating infections, reducing inflammation and healing ulcers will help reduce superficial swelling and pain, but will not cure the cancer."
Treating infections, reducing inflammation and healing ulcers will help reduce superficial swelling and pain, but will not cure the cancer. Very occasionally, spontaneous loss of blood supply to the cancer can make parts of it die but the dead tissue will still need surgical removal. The body's immune system is not effective at making these tumors to regress.
How can I nurse my pet?
After surgery, your pet will need to wear an "Elizabethan collar" to prevent damage to the operation site. Your pet may require a special diet, which will be discussed with you. Your veterinarian may request that you do not try to examine the surgery site in the early post-operative period. However, if your pet is unable to eat or develops significant swelling or bleeding at the surgical site, you need to contact your veterinarian immediately. If you require additional advice on post-surgical care, please ask.
How will I know how this cancer will behave?
The histopathology report will give your veterinarian the diagnosis that helps to indicate how it is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread), and will usually assess the completeness of excision of the tumor.
When will I know if the cancer is permanently cured?
In dogs, gingival tumors usually invade the bone and often recur locally after surgery, but few metastasize. Survival twelve months post-surgery is 44%. Tumors closer to the front of the mouth are usually easier to treat so have a better prognosis. 50% of tongue tumors recur. They metastasize to the local lymph nodes but rarely spread further.
Tonsillar squamous cell carcinomas almost invariably metastasize to local lymph nodes and two-thirds show distant metastasis, often to the lungs, although they can spread to many different organs, including the bones. They often present as a lump in the throat that may indicate they are already present in the lymph nodes. Survival time is months at the most.
These cancers have a poor prognosis in cats because of post-surgical complications. Only 20% of these cats will survive beyond 12 months. Combinations of surgery, radiotherapy, chemotherapy and hyperthermia treatments do not significantly affect survival rates. Staging of the tumor may be predictive, with greater spread at the time of surgery indicating shorter survival. Tumors at the front of the mouth, and not crossing the midline if they are in the upper jaw, have the best prognosis.
Are there any risks to my family or other pets?
No, these are not contagious tumors and are not transmitted from pet to pet or from pets to people.