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Mast cell tumours in dogs

By Nick Whittle Author

Updated on the

A mast cell tumour (MCT) is a cancer of the type of cells normally involved in the body’s response to allergies and inflammation. Learn what is in store for a dog with MCT

MCTs are the most common type of cancer found in dogs and it is estimated that one in every five canine growths are MCTs. The malignancy of a mast cell tumour ranges from ‘low grade’ to ‘high grade’, with the latter greatly limiting the animal’s life expectancy.

What causes a mast cell tumour?

There are no specific causes of an MCT but most researchers believe its presence is genetically determined. Some studies also suggest that heavier dogs are more susceptible to the illness.

In addition, a greater percentage of older dogs are presented with the disease, and some breeds (regardless of age) appear to be more at risk of developing an MCT than others.

According to Fitzpatrick Referrals, the breeds at risk include: 'Beagles, Shar Peis, Boston terriers, English bulldogs, Pugs, Labrador, Cocker Spaniels, Schnauzers, Staffordshire Bull Terriers, Rhodesian Ridgebacks, Golden Retrievers, Weimaraners and Boxers'.

What are the symptoms of a mast cell tumour?

Generally speaking, localised MCTs occur on or beneath the skin but they can also be found in other parts of a dog’s body. Superficial cancerous growths have been recorded of the eyes, mouth and throat.

Like other cancers a mast cell tumour will spread if unchecked and untreated. The propensity of the disease to spread is what determines the animal’s life expectancy. Should your dog exhibit signs of widespread cancer the outlook is bleak.

How can I tell if my dog has a mast cell tumour?

MCTs present themselves as fatty lumps on or underneath skin either covered in hair or bald. Tumour swellings can measure anything from the size of a pea to 30cm in diameter. A swelling may sometimes appear ulcerated and angry, in part due to the dog’s scratching of the lump.

A 'coming and going' of the tumour is also reported in some cases because the tumour contains changing levels of histamine.

What tests are there for a mast cell tumour?

You should be examining your dog regularly to make sure she has no obvious bumps on her body.

Use this series of simple tests to check for odd changes to her shape but bear in mind that a mast cell tumour is notoriously difficult to test for by sight. If you are concerned you should take her to a vet.

  • Check your dog’s skin, especially around her neck, face and limbs
  • Check changes in the size of any lumps you might have found
  • Check your dog for signs of systemic reactions to histamines such as vomiting and faecal blood
A dog's life expectancy depends on the spread of the mast cell tumour©Corey Motta. Unsplash

What are the veterinarian tests for a mast cell tumour?

If you suspect your dog has a mast cell tumour you should take her to the vet as soon as possible. The vet will conduct a serious of more in-depth tests. The initial test of a skin lump is by fine needle aspiration.

Following a positive diagnosis of an MCT further tests include:

  • Blood analysis: to identify at what stage is the cancer and, if applicable, to determine the prevalence of metastases or secondary growths.
  • Abdominal ultrasound or X-ray: to check the progress of the cancer (if any) and to check whether the cancer has spread to the liver and spleen.

What are the treatments of a mast cell tumour?

In the UK there are currently three methods of dealing with a mast cell tumour: surgery, chemotherapy or radiotherapy.

Surgery: Surgical removal is still considered the best treatment by most veterinarians. A complete removal of the tumour along with surrounding tissue (including nearby lymph nodes) is thought to be sufficient to prevent a reoccurrence of the cancer.

The removed tissue will be analysed to determine whether the cells around the tumour are affected. Removal of mast cell tumours that are more deeply embedded in the dog’s body requires more careful negotiation, and sufficient aftercare may be required of dogs that have undergone such procedures.

Surgery, chemotherapy or radiotherapy can treat an MCT©Matt Nelson. Unsplash

Chemotherapy: Chemical treatment is recommended for dogs that have been diagnosed with a particular aggressive mast cell tumour or metastatic tumours. The treatment may prevent the disease from travelling any further around your dog’s system but the prognosis for a dog in the advances stages of the cancer is not good.

Her quality of life will be improved by administration of anti-cancer chemicals. The side effects are not as debilitating as they are of human treatments.

Radiotherapy: For dogs with an incompletely removed tumour or recurrence of the tumour, radiotherapy is proven to be of some use. Two thirds of dogs treated with radiation lived for up to two years following treatment. A combination of chemo- and radiotherapy showed some positive results in dogs with advanced metastases.

What is the life expectancy of a dog with a mast cell tumour?

The prognosis of recovery from an MCT is determined almost entirely by the disease’s aggression. In other words dogs with MCTs that have spread to other parts of their body do not fare as well after treatment as those that have had localised MCTs or have been treated immediately prior to metastasis.

According to Willows Veterinary Centre & Referral Service, mast cell tumours of the ‘nail bed, inside the mouth, on the muzzle, in the groin area and in those sites where the skin meets mucus membranes (mucocutaneous junctions),’ are likely to hinder sufficient recovery.

Successful treatment of mast cell tumours is determined by the disease’s nature, the breed of dog and the location of the initial tumour. Early identification, diagnosis and treatment of the cancer greatly improves the animal’s life expectancy.

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