If a wound won't heal — Early symptoms and diagnosis of canine squamous cell carcinoma

Oncology/CancerDiseasesMeongsiljang Veterinary Advisory Board

Canine squamous cell carcinoma is a malignant tumor that arises from the epithelial tissues of the skin, oral cavity, toes, and nasal passages. Symptoms and prognosis vary significantly depending on the tumor's location, and early detection along with surgical removal have the greatest impact on treatment outcomes.

What is canine squamous cell carcinoma?

A puppy having its paws examined on the诊疗台 at a veterinary clinic.

Squamous cell carcinoma (SCC) in dogs is a malignant tumor that arises from epithelial tissues in the skin, mouth, toes, and nasal cavity. Symptoms, prognosis, and treatment options vary significantly depending on the tumor’s location, with the best outcomes achieved through early detection and surgical removal when feasible. If your dog has a non-healing ulcer or a new lump that persists for more than two weeks, please have it evaluated by a veterinarian right away.

Causes and major risk factors

While the exact cause of squamous cell carcinoma (SCC) remains unclear, it is known to result from a combination of the following risk factors:

Ultraviolet (UV) exposure: Repeated sun exposure on lightly pigmented skin (such as white fur or pink noses and ear tips) can cause epithelial cells (keratinocytes) to degenerate. Lack of pigment or light-colored skin is the most significant risk factor for SCC in dogs.

Actinic keratosis (solar keratosis): This is a precancerous lesion caused by repeated UV damage and is often observed in the stages leading up to the development of cutaneous SCC.

Advanced age: SCC primarily occurs in middle-aged to senior dogs over six years old, with the average age of onset reported at around nine years. However, no distinct breed predispositions have been identified.

Papillomavirus: Although viral structural antigens have been detected in some SCC cases, the virus’s precise role in the development and progression of the disease remains unclear.

Checklist of early symptoms by location

Symptoms vary depending on the affected area, but you should be alert if you notice any of the following signs:

Non-healing ulcers or scabs: Skin wounds that fail to heal within two weeks or scabs that recur repeatedly.

Firm lumps or swellings: New, firm lumps with irregular borders appearing on the skin.

Bad breath or oral bleeding: Bleeding from the gums or tongue, or a severe odor, which may indicate oral squamous cell carcinoma.

Limping: Walking with one paw held up due to swelling and pain around the toes.

Unilateral nasal discharge or epistaxis: Repeated discharge of mucus or blood from only one nostril.

A veterinarian carefully examines the skin around a puppy's toes.

Emergency signs requiring immediate veterinary attention

If any of the following apply, your pet needs to be seen in an emergency clinic within 24–72 hours: ① an oral mass that grows rapidly over a few days or interferes with swallowing or breathing; ② severe swelling of an entire toe with bleeding that won’t stop; ③ noticeable weight loss within two weeks or a sudden drop in energy. These signs suggest that a tumor may be rapidly invading surrounding tissues.

Diagnostic methods — A step-by-step guide

Fine-needle aspiration (FNA): This initial test involves collecting cells with a thin needle for microscopic examination. It is quick and simple, but used for reference rather than definitive diagnosis.

Histopathology and biopsy: This definitive diagnostic method involves removing a small tissue sample for detailed analysis. It also determines the tumor grade and depth of invasion.

CT and radiography: These imaging tests assess the extent of tumor spread into bones and surrounding tissues.

Thoracic radiography: This essential test checks for metastasis to the lungs.

Because treatment plans depend on test results, it is crucial to complete all imaging examinations.

A veterinarian performing a fine-needle aspiration on a dog's skin tumor.

Treatment options and choices

Treatment is determined by your veterinarian based on the tumor’s location, size, and whether it has metastasized.

Surgical excision: This is the most effective treatment, with wide local excision being the standard approach. Complete removal with adequate margins yields a favorable prognosis, and amputation of the affected digit can produce good outcomes for squamous cell carcinoma (SCC) of the toes.

Radiation therapy: SCC exhibits moderate sensitivity to radiation, making it suitable as a standalone treatment or as an adjunct to surgery when adequate surgical excision is difficult in certain locations.

Antineoplastic chemotherapy: Chemotherapy is generally not recommended for localized SCC. It may be considered as an adjunct for advanced, invasive, or metastatic lesions, but its efficacy has not yet been firmly established.

Photodynamic therapy (PDT) and cryosurgery: These are local treatments applied to early-stage, small, superficial lesions. They have shown effectiveness in addressing non-invasive lesions at an early stage.

A puppy recovering after surgery while wearing a neck collar

Prognosis by location — Which sites are more dangerous?

Treatment outcomes vary significantly depending on the tumor’s location and the completeness of surgical removal. Digital SCC (toes): When detected early and completely excised with adequate margins, the prognosis is generally favorable. Incomplete removal can lead to local recurrence. Cutaneous (superficial) SCC: Early, complete excision of small, non-invasive lesions results in low recurrence rates and favorable outcomes. Nasal SCC: Due to the anatomical challenges of surgical excision in this area, radiation therapy is often used alone or as an adjunct. Prognosis varies depending on the extent of tissue involvement. Oral SCC: This form is highly aggressive locally, leading to a generally poor prognosis. At the time of diagnosis, the tumor has often already invaded surrounding tissues or bone, and recurrence after treatment is common. However, the rate of distant metastasis for SCC is relatively low.

Post-surgical home care and key care points

Consistent care at home after treatment is essential for a smooth recovery.

Protect the surgical site: Use an Elizabethan collar or protective clothing to prevent your pet from licking or scratching the area.

Regular follow-up visits: Adhere to the veterinarian’s schedule for check-ups to monitor for recurrence. Seek immediate veterinary attention if you notice any new ulcers or lumps.

Sun protection: It is crucial to keep lightly pigmented areas, such as the nose and ear tips, out of strong midday sunlight. Since pet-specific sunscreens can be easily licked off and may have limited efficacy, it is best to minimize direct sun exposure and use UV-blocking curtains or shade instead.

Pain management: Administer prescribed pain medication exactly as directed, without missing any doses.

Please contact your veterinarian immediately if your pet experiences persistent loss of appetite or vomiting.

Prevention tips for owners of breeds with low pigmentation

Dogs with light-colored coats and pink skin, such as Bull Terriers, Dalmatians, and White Boxers, are at a relatively higher risk of developing squamous cell carcinoma (SCC) of the skin due to UV exposure. However, the key risk factor is the lack of skin pigment rather than any inherent predisposition of specific breeds. Avoid strong sunlight between 10 a.m. and 2 p.m., and minimize sun exposure on exposed areas like the tips of the ears and the nose. Since pet-specific sunscreens are often licked off, their effectiveness is limited; therefore, it is advisable to combine their use with shade, indoor activities, or UV-blocking curtains. Establishing a monthly habit of self-examination for the skin and oral cavity greatly aids in the early detection of non-healing ulcers, scabs, or newly formed lumps.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently asked questions

Can squamous cell carcinoma spread to other dogs or to people?

No, squamous cell carcinoma is not an infectious tumor, so it cannot be transmitted to other dogs or to people. You can safely continue living together with your pet.

If a dog’s toe is amputated due to squamous cell carcinoma (SCC), will it affect their daily life?

Most dogs adapt relatively quickly after the amputation of a single toe and are often able to walk and run normally. The remaining toes help compensate for balance, so there is usually little impact on their quality of life. However, recovery rates vary from dog to dog, so please follow your veterinarian’s rehabilitation guidelines.

What is the likelihood of recurrence after surgery?

The likelihood of recurrence varies significantly depending on whether the tumor was completely removed. If it was excised with adequate margins, the recurrence rate is low; however, incomplete removal or tumors located in the oral or nasal cavities carry a relatively higher risk of recurrence. Consistent postoperative check-ups are essential.

My dog seems to be struggling a lot during cancer treatment. What should I do?

If your pet experiences a persistent loss of appetite, severe lethargy, vomiting, or diarrhea, please contact your veterinarian immediately. These side effects can often be managed with supportive care or by adjusting the medication dosage. Do not stop the medication on your own.

What happens if the condition is left untreated?

If left untreated, the tumor can invade surrounding tissues and bones, progressing locally. Oral squamous cell carcinoma (SCC) is particularly aggressive in this regard, often causing severe pain and a rapid decline in quality of life. Therefore, it is crucial to consult with your veterinarian about treatment options as early as possible.

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References

[1] Withrow SJ, Vail DM, Thamm DH (eds). Withrow & MacEwen's Small Animal Clinical Oncology, 6th Ed. Elsevier, 2020.

[2] Dobson JM, Lascelles BDX (eds). BSAVA Manual of Canine and Feline Oncology, 3rd Ed. BSAVA, 2011.

[3] Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Veterinary Dermatopathology: A Macroscopic and Microscopic Evaluation of Canine and Feline Skin Disease. Mosby, 2005.

[4] Cowell RL, Valenciano AC (eds). Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat, 5th Ed. Elsevier, 2020.