Squamous Cell Carcinoma

TL;DR. Squamous cell carcinoma is a common, sun-linked skin and oral cancer in pets that requires early detection and aggressive treatment to manage successfully.

Older cats with white or lightly pigmented ears are highly susceptible to solar-induced squamous cell carcinoma.

What is it?

Squamous cell carcinoma (SCC) is a malignant cancer originating from the squamous epithelium, which is composed of the flat, scale-like cells (keratinocytes) that make up the outer layer of the skin and line the moist tissues of the mouth. In pets, this cancer most commonly presents in two distinct ways: as destructive, non-healing sores on the skin (cutaneous SCC) or as highly aggressive, invasive tumors inside the mouth (oral SCC).

At a microscopic level, these cancer cells break through the delicate basement membrane that separates the outer skin layer from deeper tissues, invading local blood vessels, nerves, and surrounding bone. While cutaneous SCC tends to grow slowly and is less likely to spread to distant organs early on, oral SCC is highly invasive and destructive, rapidly eroding the jawbone and surrounding oral structures.

While this disease is most frequently diagnosed in dogs and cats, it can also affect exotic species, including birds and turtles. Because clinical research and large-scale studies in these exotic species are limited, much of our medical understanding and treatment protocols for birds and turtles are extrapolated from small animal medicine. Regardless of the species, early veterinary intervention is critical to achieving a favorable outcome.

Causes & risk factors

The primary environmental trigger for cutaneous squamous cell carcinoma is chronic exposure to ultraviolet (UV) radiation from sunlight. Just as in humans, UV light damages the DNA within the skin cells, leading to mutations that cause uncontrolled cell division. Consequently, pets with white fur, light skin pigmentation, or sparse hair coats are at a significantly higher risk.

Geographic location also plays a major role; pets living in high-altitude regions or areas with intense, year-round sunlight experience much higher rates of solar-induced SCC. In cats, there is also evidence suggesting that viral infections may play a role in the development of these tumors. A leading veterinary surgery textbook notes:

"One paper suggests a papillomavirus may be involved in the etiology of feline squamous cell carcinoma. Older, white cats or those with lightly pigmented noses and that live in sunny climates are at risk. Lesions progress slowly through early solar damage with crusting and erythema to carcinoma in situ to invasive squamous cell carcinoma."

In dogs, sun-induced tumors are highly correlated with specific physical traits and lifestyle. According to a leading veterinary dermatology atlas:

"Sunlightinduced tumors on the flank and ventrum occur most commonly in lightly pigmented dog breeds such as Dalmatians, Beagles, Whippets, and White English Bull terriers. The condition is common in cats, with highest incidence reported in older white cats. The incidence of solar-induced squamous cell carcinoma is highest in geographic areas with intense sunlight."

Signs to watch for

The clinical signs of squamous cell carcinoma vary dramatically depending on where the tumor is located. Owners should regularly inspect their pet's skin, mouth, and paws for the following symptoms:

Skin (Cutaneous) Symptoms

• Crusting (Common): Persistent, scabby crusts on the ear tips, nose, eyelids, or belly that do not resolve with standard wound care.
• Erythema (Common): Localized redness and inflammation of the skin, often representing early solar damage (actinic keratosis).
• Ulcerative skin lesions (Common): Open, raw, or bleeding sores that look like infections but fail to heal.
• Proliferative skin lesions (Common): Raised, firm, wart-like or cauliflower-like growths on the skin.

Oral Symptoms

• Dysphagia (Common): Difficulty chewing or swallowing food, often causing the pet to drop food from their mouth.
• Anorexia (Common): A complete loss of appetite or refusal to eat due to severe oral pain.
• Halitosis (Common): Extremely foul breath caused by tissue death (necrosis) within the oral tumor.
• Bleeding (Common): Blood-tinged saliva or active bleeding from the mouth.

Paw and Digit Symptoms

• Swollen and painful digits (Occasional): Swelling of one or more toes, which may cause limping.
• Misshapen or absent nail (Occasional): Loss of a toenail or abnormal nail growth without a history of trauma.

Solar-induced skin lesions on a dog's belly can progress from sun damage to invasive squamous cell carcinoma.

How vets diagnose it

Your vet will begin with a thorough physical examination, paying close attention to any skin abnormalities, the oral cavity, and the lymph nodes. If a suspicious lesion is found, several diagnostic steps are required to confirm the disease and determine if it has spread.

While your vet may start with cytology (a fine needle aspirate to look at individual cells under a microscope), this test is not always definitive. As a standard veterinary cytology textbook explains:

"Because epulides are frequently composed of squamous epithelium and fibrous tissue, aspirates of these tumors are composed of variable numbers of mature squamous cells and occasional small spindle cells. The fibrous portion of the epulis is nonexfoliative or minimally exfoliative, and this causes many aspirates to be nondiagnostic because they consist entirely of blood or are almost acellular."

Because of these limitations, a biopsy with histopathologic examination is the gold standard for diagnosing squamous cell carcinoma. During a biopsy, your vet will remove a small piece of the tumor (or the entire mass) and send it to a veterinary pathologist. The pathologist will examine the tissue structure to confirm whether the cells are malignant and if they have invaded past the basement membrane.

Once SCC is confirmed, staging tests are performed to evaluate the extent of the disease:

• Regional lymph node aspirate: Cells are drawn from the nearby lymph nodes to check for early cancer spread.
• Three-view thoracic radiographs: Chest X-rays are taken to ensure the cancer has not metastasized to the lungs.
• CT scan: Particularly for oral tumors, a CT scan is highly recommended to evaluate how deeply the tumor has invaded the surrounding facial bones, which is vital for surgical planning.

Three-view chest X-rays are a critical staging test used to check if squamous cell carcinoma has spread to the lungs.

Treatment options

Treating squamous cell carcinoma requires a tailored approach based on the tumor's location, size, and whether it has spread.

Surgical Removal

For cutaneous and digital SCC, aggressive surgical removal is the treatment of choice. Your vet will aim for wide surgical margins to ensure no microscopic cancer cells are left behind. This may involve removing the tips of the ears (pinnectomy) in cats, or amputating the affected toe if the tumor is located in the nailbed. For oral tumors, surgery may involve removing a portion of the jawbone (mandibulectomy or maxillectomy).

Radiation and Hyperthermia

If a tumor cannot be fully removed with surgery—such as those located on the face or inside the mouth—radiation therapy may be used. Combining radiation with hyperthermia (localized heat therapy) has shown promising results in shrinking tumors and controlling local disease. A leading veterinary internal medicine reference notes:

"Radiotherapy plus hyperthermia has been successful"

Medical and Chemotherapy Management

Systemic chemotherapy is generally less effective for SCC than it is for other veterinary cancers, but it can still play a role in management.

• Platinum-based agents: Drugs like Carboplatin and Cisplatin (which are platinum alkylating agents) may be used by a veterinary oncologist to slow tumor progression, though their success in dogs is variable.
• Non-Steroidal Anti-inflammatory Drugs (NSAIDs): Piroxicam is frequently prescribed for pets with SCC. Beyond providing pain relief, Piroxicam has unique anti-tumor properties that can help slow the growth of the blood vessels feeding the tumor. As noted in internal medicine literature, "Piroxicam can palliate some patients with squamous cell carcinoma."

Prognosis

The prognosis for pets with squamous cell carcinoma is highly variable and depends heavily on the tumor's location.

Cutaneous (skin) SCC that is caught early and removed surgically carries a good to excellent prognosis. Many of these cases are slowly progressive, and local surgical removal can be curative, though owners must remain vigilant about sun protection to prevent new tumors from forming.

Conversely, oral SCC carries a guarded to poor prognosis, particularly in cats. These tumors are highly invasive, making complete surgical removal difficult. While treatment can improve quality of life and provide comfort, long-term survival times for oral SCC remain short.

For exotic species like birds and turtles, long-term prognosis data is limited due to a lack of published clinical trials. Treatment in these species relies on aggressive local therapy, and outcomes depend heavily on how early the disease is detected.

Prevention

While you cannot change your pet's genetics, you can take active steps to prevent solar-induced cutaneous squamous cell carcinoma:

• Limit sun exposure: Keep white-furred, light-skinned, or sparsely haired pets indoors during peak UV hours, typically between 10:00 AM and 4:00 PM.
• Apply pet-safe sunscreen: Use sunscreens specifically formulated for pets on vulnerable areas like the bridge of the nose, belly, and ear tips. Never use human sunscreens containing zinc oxide or salicylates, as these are highly toxic if licked.
• Install UV-blocking window films: If your pet loves to sunbathe indoors, apply UV-blocking films to your windows to protect them from harmful rays.
• Perform regular skin checks: Routinely inspect your pet's skin and mouth for any new crusts, redness, or sores.

When to call your vet

You should schedule a veterinary appointment if you notice any persistent redness, crusting, or non-healing sores on your pet's skin, ears, or nose.

Immediate veterinary attention is required if your pet exhibits severe bleeding from the mouth, sudden difficulty swallowing, rapid weight loss, or signs of extreme pain, such as vocalizing or refusing to walk on a swollen toe.

For specific breeds

Certain breeds are genetically predisposed to developing squamous cell carcinoma, particularly those with light skin or sparse coats. Owners of the following breeds should practice strict sun safety and perform frequent skin checks:

• Dalmatian
• Beagle
• Whippet
• Bull Terrier (especially the White English Bull Terrier)
• Labrador Retriever
• German Shepherd Dog
• Poodle (including the Standard Poodle)

Sources

• Small-Animal Dermatology: A Color Atlas and Therapeutic Guide, pages 441, 444.
• Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat, 5th Edition, page 153.
• Current Techniques in Small Animal Surgery, 5th Edition, page 392.
• Textbook of Veterinary Internal Medicine, 5th Edition, page 464.