Squamous Cell Carcinoma in Dogs
Squamous cells line the epidermis, which is the outermost part of the skin. A tumor of the skin cells is called a squamous cell carcinoma (SCC). This type of cancer can occur anywhere this type of cell is present. In dogs, the most common sites of SCC are the skin, nail beds, and oral cavity. Squamous cell carcinoma accounts for less than five percent of skin tumors in dogs. Twenty-five percent of mouth tumors in dogs are also attributed to SCCs. It may develop anywhere in the dog’s oral cavity, including the tongue, gums, lips, tonsils, and mucus membranes. Continue reading to learn more about the symptoms and treatment options for SCC in dogs.
Causes of Squamous Cell Carcinoma in Dogs
Several factors can increase the risk of dogs developing SCC. These include:
- Older dogs are at greater risk for developing SCC. The average age of SCC occurrence in dogs is between 8-10 years old.
- Prolonged exposure to solar UV radiation. Exposure to the sun’s ultraviolet rays is a very common predisposing factor of SCC in dogs.
- Lack of skin pigment
- Sparse hair coat
- Carcinogens and environmental pollutants
- Dogs with dark hair coats appear to have a high risk of digital (toe/paw) tumors.
Symptoms of Squamous Cell Carcinoma in Dogs
Most SCCs tend to be localized. But there are cases in which the tumor invades the bone tissues. Tumor spread to adjacent lymph nodes may also occur. However, metastasis to distant organs is rare and usually doesn’t take place until the condition is well-advanced.
The appearance of SCC tends to be variable and non-specific. The tumor may appear shallow and crusting, deeply ulcerated, red and proliferative, or cauliflower-like.
The appearance of the tumor may change as it develops. There have been cases in which the tumor has been misdiagnosed as inflammation or traumatic lesions and was prescribed antibiotics and corticosteroids.
The symptoms of SCC depend to a large extent on the location of the tumor. Dogs with digital tumors may exhibit lameness and digit ulceration. If SCC affects the nose and nasal passages, there may be facial deformity, sneezing, and nasal discharge. Dogs with oral SCC may show bleeding in the mouth, excessive salivation, loss of appetite, weight loss, bad breath, and loose teeth.
Diagnosis of Squamous Cell Carcinoma in Dogs
Early detection and diagnosis are of paramount importance so appropriate therapeutic intervention can be started immediately. This may increase the chance of long-term control or even be curative for affected dogs.
Your vet may suspect SCC based on the appearance of the growth and where it’s located.
Microscopic exam (cytology) of tissues from the tumor can help arrive at a definitive diagnosis. Biopsy and laboratory exam of the collected tissues (histopathology) may be required if the initial microscopic exam is inconclusive.
Treatment Options and Prognosis
Early diagnosis of squamous cell carcinoma is very important to achieve a better prognosis. The smaller the tumor and the earlier the stage, make them the most amenable to treatment.
There are several treatment options for SCC in dogs. If surgery is not possible or feasible, your vet may recommend adjuvant therapies to lessen the chance of SCC from coming back.
Local Treatment Options for SCC in Dogs
- Surgery - This is often regarded as the best treatment option for most patients. It has been shown to provide the longest disease-free interval when compared to radiation therapy and cryotherapy. Surgical amputation of dogs with digital SCC tumors can increase the chance of keeping the tumor completely controlled.
- Cryotherapy - This is indicated for small, superficial tumors that can’t be completely removed with surgery. Its advantages include being inexpensive, readily available, and the results are cosmetically excellent.
- Radiation therapy (RT) - This is a primary treatment option for inoperable tumors or tumors that have been incompletely removed. It’s the most common procedure indicated for SCC of the nasal and oral cavity. The best response is achieved when tumors are still in the early stage.
- Plesiotherapy - The procedure involves applying topical radiation to the tumor. Its use is limited to superficial tumors or tumors that can’t be completely removed with surgery.
- Photodynamic therapy (PDT) - A photosensitizer is administered topically or intravenously to accumulate in the tumor cells. Once the growth is exposed to light of a specific wavelength, the photosensitizer is activated and causes the death of tissues.
- intratumoral chemotherapy - While chemotherapy is generally not considered for SCCs because the chemo-responsiveness of the tumors is very low, the procedure may be considered in certain cases. Chemotherapy for SCC may be recommended for tumors that are metastatic, rapidly growing, or inoperable.
Systemic Therapy Options for SCC in Dogs
Chemotherapy, COX-2 inhibitors, and other systemic therapy options may be recommended for canine squamous cell carcinoma in the following cases:
- Growth is inoperable
- The tumor is poorly differentiated
- Metastasis is already present at the time of diagnosis
- Mass is in a location known for aggressive biologic behavior.
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