Skin squamous cell carcinoma in dogs: symptoms and treatment

Overview

Squamous cell carcinoma is abbreviated to SCC. In dogs, cutaneous and subungual forms are distinguished. A subungual tumour starts in the nail bed epithelium. It is therefore a tissue-originating cancer even if the initial signs resemble inflammation.

Most tumours are solitary. However, several separate tumours can develop on sun-damaged skin. This cancer typically invades surrounding soft tissues and may enter bone. Metastases from the cutaneous form are generally uncommon but can occur in nearby lymph nodes, for example.

Among all canine skin tumours, SCC is relatively uncommon. It can also affect the pads, ears or nose.

Causes

Sun-damaged skin

The precise cause of most individual tumours is unknown. Some cutaneous tumours arise after chronic sun damage. Sparsely haired, lightly pigmented skin has little protection from UV radiation. Abdominal skin can be exposed when a dog lies on their back in the sun. Radiation reflected from the ground may also contribute to abdominal lesions.

Before cancer develops, actinic keratosis, a sun-induced keratinisation change, may appear. Affected skin can become red, thickened and excessively keratinised. Changes may also involve skin colour.

Not every form is sun-related

The association between subungual cancer and a dark coat differs from the risk affecting pale, sun-damaged skin. Some cutaneous SCCs develop without tissue evidence of sun damage. A rare multicentric skin form may be associated with papillomavirus-induced changes. A common papillomavirus skin wart can also rarely become invasive SCC, growing into surrounding tissue.

Unusually high KITLG gene expression has also been associated with subungual cancer susceptibility in Schnauzers.

Risk factors

Cutaneous SCC is usually diagnosed in older dogs. Pale skin and a short, sparse coat predispose dogs to the sun-associated form. Breeds with these tumours include Dalmatians, Bull Terriers and Beagles.

An Australian study compared 295 dogs with cutaneous SCC against 1,180 controls; diagnoses were confirmed by tissue samples. Dogs aged 7–11 years had an odds ratio of 7.4 compared with those aged 2–6 years. For dogs aged at least 12 years, the corresponding value was 4.8.

Breeds predisposed to subungual SCC include Giant Schnauzers, Standard Schnauzers, Gordon Setters, Briards and Scottish Terriers. A dark coat is common among dogs with these tumours.

Digital tumours are diagnosed at an older average age in Miniature Schnauzers than in Standard or Giant Schnauzers. Among Giant Schnauzers, males have shown greater susceptibility.

Multiple digital SCCs have been identified more often in Standard than Giant Schnauzers.

Typical symptoms

A tumour can appear on the head, lower limbs, underside of the abdomen or around the anus and genitals. A skin lesion may resemble ordinary irritation or an ulcer.

• A firm, raised lump develops.
• There is a thickened, plaque-like skin lesion.
• The surface ulcerates or becomes crusted.
• The tumour may project outwards as a wart-like growth.
• A claw changes shape, splits or detaches.
• Your dog limps, has a tender toe or avoids walks.
• Your dog licks or chews the affected toe.

A toe may leave blood marks on the floor. A subungual lesion can resemble longstanding nail or bone infection. Tumours may affect several toes on different limbs.

The toe or nail bed can look swollen and inflamed without a distinct lump. A tumour-associated claw change may persist despite antibiotics.

Complications and consequences

Local growth and spread

Tumour ulceration can be painful. Broken skin may develop secondary bacterial infection. A nail bed tumour can destroy the terminal toe bone. Digital cancer can spread to regional lymph nodes and lungs. Metastases identified initially are associated with a poorer outlook.

A well-differentiated tumour resembles its original tissue microscopically and generally progresses more slowly. Poorly differentiated tumours can recur or metastasise within 20 weeks of removal. Treatment failure is often associated with late recognition and difficulty controlling local growth.

Outlook depends on the form

Among 193 dogs with cutaneous SCC, median overall survival was 1,004 days: the point at which half remained alive. For tumours with solar damage, the median was 1,359 days. Without these changes, it was 680 days.

Among 79 dogs undergoing digital tumour surgery, cancer-specific survival was 81% at 1 year and 60% at 2 years. New, separate digital SCCs developed in 22.8% of dogs followed up. Local recurrence after toe amputation occurred in 3.8%.

New, separate digital tumours were diagnosed a median of 190 days after the original surgery. Symptoms persisting over 90 days were associated with a shorter interval to progression.

Diagnosis at the vet

Sampling distinguishes cancer from inflammation

Tumour type cannot reliably be identified by palpation or imaging alone. A fine-needle sample collects cells for microscopic examination. If cytology is inconclusive, a biopsy is taken. Tissue examination reveals tumour structure and may help assess behaviour.

A persistent toe or claw lesion unresponsive to initial treatment warrants biopsy. If a paw tumour is suspected, X-rays can help investigate bone and surrounding changes. Biopsy also allows assessment of differentiation and invasion. After surgery, tissue examination assesses whether removal margins are clear.

Assessing spread

Your vet measures the tumour and checks whether it moves or is attached to surrounding tissues. A deep lesion may need X-rays, ultrasound or CT. A normal-sized lymph node does not exclude metastases. Fine-needle sampling or tissue examination establishes whether it contains tumour cells.

Chest X-rays can look for metastases. Abdominal ultrasound or other imaging is chosen according to whether findings would change treatment or the outlook. A blood count, blood biochemistry and urine sample help assess general health.

Tumour grade describes the microscopic appearance of cells and tissue. Stage describes local extent and regional or distant metastases. An enlarged node may also reflect inflammation, so sampling clarifies the finding. Special stains may be needed if routine tissue examination cannot determine tumour type.

Among the 79 surgical digital tumour patients, 92.4% showed bone destruction on imaging. Cytology results may be available in 0–2 days. Tissue examination results usually take 3–7 days.

Lymph node cytology can be negative despite early tumour involvement. Finding metastases may change both treatment options and the outlook.

Treatment

Surgery removes the local tumour

Your vet plans treatment according to tumour type, spread and your dog's circumstances. Surgical removal is first-line treatment for localised cutaneous SCC. The aim is complete removal without leaving cancer cells at the site. A margin of at least 2 cm around a skin tumour is generally recommended.

A subungual tumour is usually treated by amputating the affected toe. A very large digital tumour may require amputation of the entire limb. Closure after tumour removal is planned to minimise tension and preserve function. The removed tissue is marked so the pathologist can identify the margins. Imaging-visible markers may be left at the surgical site to guide later radiotherapy.

Other cancer treatments and symptom relief

Radiotherapy may be considered alongside surgery if complete removal is impossible. Canine skin and nasal planum SCC generally respond less well to radiotherapy than surgery. There is no firm evidence of additional chemotherapy benefit for every dog with cutaneous SCC. Medication may be considered for digital tumours particularly when metastases are identified.

A painful toe or ulcerated tumour may need prescribed pain relief. Secondary bacterial infection is treated with a vet-selected antibiotic if needed. Prevent licking and chewing to avoid further damage.

Follow-up after treatment

Checks look for local recurrence, metastases, new tumours and treatment adverse effects. Intervals depend on diagnosis, your dog's condition and time since treatment ended. After radiotherapy, checks often take place every 2–4 weeks during the first 2–3 months. They may then occur every 2–3 months during the first year.

In the second year after radiotherapy, checks may take place every 3–6 months.

Prevention

Reducing excessive UV exposure may prevent sun-associated cutaneous SCC. Keep susceptible dogs out of the strongest direct sunlight. UV-reducing window film may lower exposure through glass.

Have thickened or discoloured skin examined before it ulcerates. At-risk dogs' toes are also checked at annual veterinary visits. All claws and toes need regular monitoring after a previous digital tumour.

A suitable animal sunscreen can be combined with protection against sun-related skin damage. Prolonged sun exposure in short-haired dogs increases exposure and is associated with greater disease frequency.

Important for dog owners

Monitor every claw, including those on previously unaffected limbs. Arrange reassessment if a claw changes shape or a toe causes lameness and initial treatment does not help. Watch bleeding, pain and willingness to exercise when a lesion ulcerates.

Keep the pathology report and ask whether margins were clear. Request an individual plan for monitoring new lesions and possible recurrence. A new tumour at another site remains possible after successful removal.

Frequently asked questions

Is a non-healing wound always skin cancer?

Appearance alone cannot establish whether a lesion is a tumour. However, SCC can appear as an ulcerated or red skin area. Cytology or biopsy of a persistent lesion helps distinguish cancer from other causes and plan appropriate care.

Can a detached claw indicate a tumour?

Subungual SCC can cause claw deformity, inflammation and detachment. The toe may be very painful and cause lameness during walking. If initial treatment fails, biopsy is needed to avoid diagnostic delay.

Can surgery cure SCC?

Complete removal of a localised skin tumour can provide long-term control. For the subungual form, this usually requires amputation of the affected toe. Differentiation and possible metastases also inform the outlook, so the tumour name alone does not determine outcome.

Can a dark-coated dog develop this cancer?

Dark-coated dogs can develop SCC, particularly beneath the claws. Predisposed breeds include Giant and Standard Schnauzers. The solar risk of pale, sparsely haired skin represents a different presentation, so a dark coat does not remove the need to investigate persistent claw changes.

Can a new tumour appear in another toe?

New, separate digital tumours can develop even after successful surgery. They can affect toes on different limbs. Regular checks of all claws and prompt investigation of changes therefore remain part of follow-up even when the original surgical site is healthy.