Mast Cell Tumours in Dogs: Causes, Symptoms, and Treatment

Mast cell tumours (MCTs) are one of the most commonly diagnosed skin cancers in dogs. They develop from mast cells, which play a key role in the body’s immune response. Although these tumours can appear almost anywhere on a dog’s body, they often grow on or just beneath the skin. 

Early diagnosis and timely treatment can significantly improve a dog’s prognosis. In this article, we’ll explore the causes, common symptoms, diagnostic methods, and treatment options for mast cell tumours in dogs.

What Are Mast Cell Tumours?

Mast cell tumours arise when mast cells—a type of white blood cell found in connective tissue—begin to proliferate uncontrollably. These cells store and release various chemical mediators (such as histamine), which can trigger inflammatory reactions within the body.

Appearance & Location

MCTs often appear as raised lumps or nodules in the skin but can also be found in subcutaneous tissue (just beneath the surface). Less commonly, they develop internally.

Aggressive Potential

Some mast cell tumours remain relatively stable, while others may be quite aggressive and spread (metastasise) to lymph nodes, spleen, liver, or bone marrow. The location and histological grade of the tumour often influence the prognosis.

Causes & Risk Factors

The exact cause of mast cell tumours is not fully understood, but there are certain risk factors and breed predispositions:

Breed Susceptibility

Some breeds have a higher incidence of MCTs. These include:

• Boxers

• Pugs

• Bulldogs

• Boston Terriers

• Golden Retrievers

Genetic Factors

Inherited mutations or genetic predispositions are suspected in some lines of high-risk breeds.

Age & Environment

MCTs are more frequently diagnosed in middle-aged to older dogs, although they can occur at any age.

Immune factors may also play a role.

While these factors may increase the likelihood of mast cell tumours, any dog can develop an MCT.

Common Symptoms

Because mast cell tumours can release histamine and other chemicals, they can cause a range of signs:

Skin Lumps or Bumps

• Typically the most obvious sign: a single lump or multiple nodules.

• Can vary in size, texture, and colour; some swell intermittently or become inflamed.

Ulceration or Bleeding

• The surface of the tumour may break down, leading to bleeding, weeping, or crusty lesions.

• Licking or scratching the affected area can worsen irritation.

Gastrointestinal Issues

• Vomiting, diarrhoea, or decreased appetite may occur when a tumour releases excessive histamine.

• In severe cases, stomach ulcers can develop.

Localised Swelling (Darier’s Sign)

• A peculiar characteristic of mast cell tumours is swelling or redness around the tumour if it is manipulated or touched.

If you notice a new lump or any significant change in your dog’s skin, consult your veterinarian promptly for an evaluation.

Diagnosis

Your vet will perform a thorough examination of your dog, potentially followed by several diagnostic steps:

Fine Needle Aspiration (FNA)

• A small sample of cells is withdrawn from the lump using a fine needle.

• Quick, minimally invasive, and often the first-line diagnostic procedure.

Biopsy

• A surgical biopsy may be necessary if FNA results are inconclusive, or to gain a more comprehensive assessment of the tumour’s nature.

Staging Tests

• Blood tests, ultrasound, or x-rays might be carried out to determine if the cancer has spread to the lymph nodes or internal organs.

• This “staging” helps guide treatment decisions and predict outcomes.

Histopathology & Grading

• Once removed or sampled, tumours are sent to a pathologist.

• A grade (low, intermediate, or high) indicates the potential aggressiveness of the MCT.

Accurate diagnosis and grading are crucial to developing an effective treatment plan.

Treatment Options

Treatment for mast cell tumours typically depends on the grade, stage, location, and overall health of the dog. Common approaches include:

Surgical Removal

• Often the first and most definitive step in treating accessible MCTs.

• A margin of healthy tissue around the tumour is removed to reduce the chance of regrowth.

Radiation Therapy

• May be used after surgery if the tumour margins are not clear, or if surgery is not feasible due to the tumour’s location.

• Can also be a palliative treatment for inoperable or metastatic tumours.

Chemotherapy

• Recommended for high-grade or metastatic mast cell tumours, or in conjunction with surgery to minimise recurrence.

• Drugs used may include vinblastine, lomustine, or corticosteroids (e.g., prednisone).

Targeted Therapies

• Recent advances in veterinary medicine have led to targeted drugs (e.g., tyrosine kinase inhibitors like toceranib) that help block the signals that promote cancer cell growth.

Tigilanol Tiglate

• A relatively new advancement in the treatment of MCTs in dogs

• Suitable for MCTs on the skin surface anywhere on the body, and those under the skin on the limbs

• Offers a non-surgical alternative to treatment, though most dogs will need some sedation for the treatment.

Supportive Care

• Medications to control histamine release (e.g., antihistamines and antacids) can help alleviate gastrointestinal symptoms and prevent complications such as stomach ulcers.

• Pain management, nutritional support, and anti-inflammatory treatments may also be essential.

Collaborating with a veterinary oncologist can help ensure your dog receives the most suitable combination of these therapies.

Prognosis & Life Expectancy

The prognosis for dogs diagnosed with mast cell tumours varies widely. Some key factors include:

Tumour Grade

Low-grade (Grade I) MCTs are less likely to spread and often respond well to surgical removal. Survival can be measured in years if completely excised.

High-grade (Grade III) MCTs are more aggressive; they metastasise more readily and typically require a combination of treatments. Prognosis is guarded without aggressive treatment.

Tumour Location

MCTs near vital structures, such as the face, muzzle, or around the anal area, can be more challenging to remove surgically.

Internal tumours often present a more complex treatment scenario.

Overall Health

Dogs in good general health may tolerate treatment (surgery, chemotherapy, or radiation) better and experience fewer complications.

In many cases, early detection and prompt surgical intervention lead to a very favourable outcome, especially for low-grade MCTs.

Prevention & Early Detection

There is no guaranteed way to prevent mast cell tumours, particularly because some breeds are genetically prone. However, you can improve the chances of early detection and successful treatment by:

Performing Regular Home Checks

Gently run your hands over your dog’s body during grooming or play to feel for any new lumps, bumps, or skin changes.

Scheduling Routine Vet Visits

Your veterinarian can identify suspicious growths and recommend diagnostic testing if necessary.

Monitoring Known Lumps

If your dog already has benign growths or MCTs, keep track of changes in size or appearance and report them promptly.

Final Thoughts

Mast cell tumours in dogs can range from easily treatable low-grade growths to aggressive, life-threatening malignancies. The key is early detection, accurate diagnosis, and timely treatment. If you spot any unusual lumps or notice changes in your dog’s existing growths, schedule an appointment with your veterinarian straight away. 

With vigilant monitoring, rapid intervention, and appropriate therapy, many dogs with mast cell tumours can go on to enjoy healthy, active lives.