Squamous cell carcinoma in dogs.

What it is

Squamous cell carcinoma (SCC) arises from the keratin-producing cells of the skin and mucous membranes. In dogs, three clinical presentations are most common: oral (gum/tonsil/tongue), subungual (under the toenail), and cutaneous (often UV-related, on sparsely-haired skin).

Each form behaves somewhat differently. Oral SCC and tonsillar SCC can be locally aggressive and have moderate metastatic risk; subungual SCC of the digit tends to be locally aggressive with later metastasis; cutaneous SCC on sun-exposed skin tends to be the most indolent of the three when caught early.

Signs to watch for

• An oral mass, drooling, or blood-tinged saliva. Oral SCC.
• A persistent toe swelling or lost toenail that won't regrow. Subungual SCC — often misdiagnosed as a chronic infection first.
• A non-healing skin lesion in a thin-coated area (belly, eyelids, inner thighs) — particularly in light-skinned breeds.
• Persistent skin redness or scaling in sun-exposed areas.

How veterinarians diagnose it

Biopsy is the standard — FNA can be suggestive but tissue confirms the diagnosis and assesses invasion. Subungual SCC often requires amputation of the affected digit for both diagnosis and treatment.

Staging is location-dependent: regional lymph node aspiration for oral and subungual SCC, chest radiographs or CT for moderate-to-large or higher-grade lesions, and bone radiographs of the affected limb for subungual disease to assess for underlying bone invasion.

What treatment usually looks like

• Wide surgical excision is the foundation. For oral SCC, this may mean mandibulectomy or maxillectomy. For subungual SCC, digital amputation is standard. For cutaneous SCC, wide excision with appropriate margins.
• Radiation therapy as an adjunct for incompletely excised tumors or as definitive therapy for unresectable disease.
• NSAIDs (piroxicam) have shown anti-tumor activity in some canine oral SCCs.
• Chemotherapy (carboplatin, mitoxantrone) for high-risk or metastatic disease — variable response.
• Photodynamic therapy or topical 5-FU may be options for some superficial cutaneous lesions at specialized centers.

Prognosis

Outcomes vary substantially by location and stage. Surgically excised cutaneous SCC with clean margins often has excellent long-term outcomes. Subungual SCC of a single digit with timely amputation has good outcomes; multiple-digit disease is more concerning. Oral SCC outcomes depend on size, location (rostral lesions do better than caudal), and lymph node status.

Tonsillar SCC is the most aggressive variant with the shortest median survival even with combined-modality treatment.

Questions to ask your vet

• What variant are we dealing with — oral, subungual, cutaneous, or tonsillar?
• Has the disease been staged appropriately for the location?
• Is surgical excision feasible with clean margins? What functional impact will it have?
• Do we need radiation as an adjunct?
• Is piroxicam appropriate for our case?

Where to learn more

Veterinary teaching hospitals at most accredited US vet schools maintain owner-facing fact sheets on common cancers. Peer-reviewed journals — JAVMA, Veterinary and Comparative Oncology, Frontiers in Veterinary Science — are accessible through PubMed. The American College of Veterinary Internal Medicine (ACVIM) and the Veterinary Cancer Society publish consensus statements you can ask your vet to walk you through.

For clinical trials enrolling dogs with this diagnosis, see the SciRouter Vet trial finder — we index AVMA, NCI COTC, and twelve university registries.