Skin Cancer (Squamous Cell Carcinoma) in Dogs

A squamous cell carcinoma is a cancer of the epidermal cells in the skin of dogs. This is a malignant tumor, but metastasis to other parts of the body is rare, especially with cutaneous tumors. Squamous tumors account for only about 5% of all cutaneous tumors in dogs. Subungual squamous tumors in the nail bed are more common and have a higher rate of metastasis to the lymph nodes and lungs. Most tumors appear as a raised lump with a rough surface resembling a wart. Tumors are usually inflamed and may bleed and become infected, especially if a dog scratches or digs at the tumor. Concurrent bacterial or fungal infection is possible, and the local lymph nodes often become inflamed, depleting the immune system, and making it easier for the cancer to metastasize. Subungual tumors on the nail bed often result in loss of the nail, and dogs may show signs of limping and lameness. These tumors may spread into bone and the nerve cells and are more difficult to remove permanently with surgery than cutaneous tumors. Squamous tumors can also occur in the epithelial layer of the gastrointestinal tract, especially in the oral cavity. Depending on the location of the tumor, oral squamous carcinoma can interfere with swallowing or cause mild cough. Tumors on the tonsils and tongue have a higher rate of metastasis, while those in the nasal cavity are more likely to remain contained. Surgery is frequently an effective treatment for squamous cell carcinomas, unless metastasis to the lungs or lymph nodes is already present at the time of diagnosis.

Cancerous tumors that form on the epidermal layer of the skin are called squamous cell carcinoma. This type of tumor can be found in several locations, either directly on the skin, in the nail bed area of the toes, or in the oral cavity. Squamous cell carcinoma has a low rate of internal metastasis, so it is more treatable than many other forms of cancer.

Symptoms may vary depending on the location of the tumor.

• Raised wart like lump
• Inflamed sores
• Bleeding sores
• Limping or signs of pain when walking
• Lameness
• Excessive drooling
• Difficulty chewing or swallowing
• Mild cough
• Swollen or inflamed areas in the mouth
• Loose teeth
• Oral bleeding

Types

Squamous cell carcinomas are defined by their location on the body.

Cutaneous squamous cell carcinoma (actinic keratosis)

• Tumors that occur in the skin especially hyper-pigmented areas with a high rate of exposure to sunlight
• More common in Keeshonds, Standard Schnauzers, Basset Hounds and Collies.

Subungual squamous cell carcinoma

• Tumor in the epithelial layer of the nail bed, this is the most common form of squamous cell carcinoma, accounting for about 50% of digital tumors in dogs
• A slightly higher number of females are affected
• Breeds with increased incidence include Giant, Standard and Miniature Schnauzers, Gordon Setters, Standard Poodles, Scottish Terriers, Labrador Retrievers, Rottweilers, and Dachshunds

 Oral Squamous cell carcinoma 

• Squamous tumor that occurs in the mouth, more common in older neutered females
• Breeds with increased incidence include English Springer Spaniels and Shetland Sheepdogs

It can be difficult to pinpoint the exact cause of cancer since many genetic and environmental factors probably play a part. These are some of the conditions which may put your dog at an increased risk of developing squamous cell carcinoma.

• Age – the mean age for diagnosis of squamous cell carcinoma is between 6 and 11 years old; risk generally increases with age
• Exposure to sunlight – this is less obvious than it is with humans, but outdoor dogs are more at risk
• Short haired dogs
• Dog with dark colored coats
• Large breed dogs
• Papilloma virus

Squamous cell carcinoma resembles many other skin tumors, so the veterinarian will need to examine a sample of the tumor with cytology to make an accurate diagnosis. A biopsy or needle aspirant will be taken with a local anesthetic. In some cases, the veterinarian may decide to surgically remove the tumor first, and diagnose the cancer microscopically after removal.

Bloodwork will likely be taken to evaluate your dog’s immune system and check for signs of systemic illness from metastasis. Dogs with affected lymph nodes may show a low lymphocyte count on a blood test. X-rays may also be necessary to check for metastatic tumors in the lungs, especially with subungual squamous carcinoma.

Surgical excision is the most effective treatment for squamous cell carcinoma. A 2cm margin around the tumor will be needed to ensure the removal of all cancerous tissue. With subungual tumors, this usually involves removing the entire digit. Since squamous cell carcinomas are skin tumors, most surgeries are minimally invasive. You will need to clean and check the area regularly after surgery, and try to keep your dog from scratching at the incision. A return check-up may be needed several weeks later.

There are a few alternative treatments if your dog is not healthy enough for surgery, or if the cancer is still in the very early stages. Intralesional implant chemotherapy is the insertion of a sustained release gel implant containing a chemotherapy medication such as fluorouracil or cisplatin. This treatment has had a reasonable success rate with squamous cell carcinoma in dogs. Etretinate, a medication that is sometimes used for very severe psoriasis, has also been effective at treating squamous cell lesions in the early stages. This is less effective on lesions that are very aggressive, and treatment may have to be carried out for up to ninety days.

Squamous cell carcinoma treatment has a much higher success rate than other forms of cancer, as long as the tumor has not metastasized to other areas of the body. Studies have found that 95% of dogs that have surgery on a squamous cell carcinoma survive for at least one year after surgery. With repeat surgery on subungual tumors, 60% of dogs still survived for at least one year; however when internal metastasis was present, the survival rate at one year was only 10 %. Like most forms of cancer, a complete cure is rare, but this type of cancer is usually treatable as long as it is caught in the early stages.