What is an oral squamous cell carcinoma?
A squamous cell carcinoma (SCC) is a malignant tumor of the cells that line the outer layer of the skin (the epidermis), and the passages of the respiratory and digestive tracts.
Squamous cell carcinoma is the most commonly reported oral tumor in cats, and the second most common in dogs. This cancer can also affect the tonsils in dogs and cats (called tonsillar SCC), as well as the gum line and remainder of the oral cavity (mouth).
Multicentric squamous cell carcinoma (also known as Bowen’s disease or Bowenoid carcinoma) is a type of squamous cell carcinoma that occurs in both dogs and cats. The lesions are confined to the surface layers of the skin and mouth. Multicentric SCC is rare in cats and dogs.
What causes this cancer?
The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
In cats, exposure to smoke, as well as the use of flea collars have been identified as significant risk factors for the development of squamous cell carcinoma. In dogs, no such correlation has been made, but may be possible. UV exposure has also been proposed as a risk factor in the development squamous cell carcinoma of the skin covering the nostrils.
Recent studies have shown that exposure to papilloma-like viruses may to contribute to the development of multicentric SCC in the mouth.
What are the clinical signs of squamous cell carcinomas?
Lesions may appear as diffusely thickened, plaque-like areas, or may be more nodular or cauliflower-like in appearance, arising from any location within the mouth. Others may be associated with the gum line, may be pink or discolored, and may ulcerate (break open and bleed). These tumors may look small but may actually extend deeper into the tissues than expected, invading the underlying bone.
Your pet’s clinical signs will depend on the location, tumor type, tumor size, and presence of spread. Oral pain is usually apparent, especially in pets with tumors that have penetrated the underlying bone. This may cause signs such as excessive salivation, excessive panting, bad breath (halitosis), lack of appetite, difficulty eating, and reluctance to be touched on the head. Secondary infections are also common.
Swelling of one or both tonsils occurs with tonsillar SCC resulting in difficulty breathing and problems with swallowing.
How is this cancer diagnosed?
Fine needle aspiration (FNA) or biopsy will be performed. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.
In some cases, results from FNA may not be entirely clear and biopsy may be necessary. A biopsy is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave (probability of local recurrence or spread to other areas).
How does this cancer typically progress?
Oral SCC in the cat is locally aggressive, meaning it will invade the underlying and associated tissues close to the tumor. This poses the biggest risk for your cat. The risk of spread elsewhere is considered quite low, but in cats the actual rate is unknown. Multicentric SCC is locally invasive and if caught early can be much easier to treat. However, spread is possible.
In dogs, oral SCCs tumors are also locally aggressive.
Tonsillar SCC is much more aggressive and can metastasize (spread elsewhere in the body), with more than 75% of cases exhibiting spread to local lymph nodes or elsewhere in the body.
In both cats and dogs, staging (searching for potential spread to other locations in the body) is highly recommended for malignant tumors, as they tend to spread. This may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. If any lymph nodes are enlarged or feel abnormal, further sampling by FNA may be pursued to determine if spread is present.
What are the treatments for this type of tumor?
Surgical removal is the standard method for treating SCCs in both dogs and cats. The prognosis in dogs for surgical success is greater than cats. Squamous cell carcinoma affecting the tongue in cats carries a poor prognosis. CT scans of the head/neck are helpful to be performed prior to surgery to determine the extent of disease, as well as for surgical planning. If lymph nodes under the jaw (mandibular lymph nodes) are affected, they will typically be removed during surgery.
Depending on how invasive the tumor is, surgery may involve removing a portion of your pet's jaw (upper or lower). Although this type of surgery sounds daunting for you and your dog, many of these tumors are painful and surgical removal provides relief.
After surgery, the tissues are sent for histopathology to predict, as best as possible, the probability of local recurrence or metastasis (spread to other areas). If the entire tumor is submitted, the pathologist may be able to assess if the tumor was completely removed or if additional therapies (a second surgery, radiation, or chemotherapy) are necessary.
Depending on the results of the histopathology, radiation therapy may be recommended following surgery.
In some cases, surgery may not be possible or warranted. Radiation or other therapies may be pursued in these cases to help keep your pet comfortable.
In pets with tonsillar SCC, surgical removal of the affected tonsil(s), and the associated lymph nodes is usually pursued. Chemotherapy following surgery may be recommended given the tendency for tonsillar SCC to metastasize.
In cases of metastasis of SCC, chemotherapy is usually recommended.
Is there anything else I should know?
These tumors cause inflammation and pain. While your pet is waiting for surgery, pain control and reducing inflammation can bring some relief.