Mast cell tumours in dogs

Mast cell tumours (MCT) are the most common type of skin cancer in dogs. They can also affect other parts of the body, directly or indirectly, and cause life-threatening disease. Surgery is the best option when possible, but other treatments can also help.

Up to one in five skin tumours in dogs will be an MCT. Not all of them will spread, but they can also cause allergic-type reactions or gastric ulcers. They often start as a red nodule or lump on or under the skin but can have many different appearances. Milder MCT can often be cured with surgery. If aggressive or already spread, treatment is difficult and may only work temporarily. Around 15% of dogs will go on to develop other MCT after successful treatment of one. Always discuss skin lumps with a vet, especially if there is redness, itchiness or discomfort.

Overview

What are mast cell tumours in dogs?

Mast cells are one of the border guards of the immune system. They are in charge of releasing substances that prepare the body to respond when an invader or an injury is detected. Unfortunately, they can suffer mutations and turn cancerous.

Some MCT will be very aggressive and quickly spread to lymph nodes and other organs.
Others will just grow slowly in place for a long time.
Both types can produce excess histamine and other signal molecules, affecting the surrounding skin and even distant organs such as the stomach.
If a lot of these substances are released suddenly, it causes the same effect as a severe allergic reaction.

Speak to a vet if your pet has a lump that is bothering them or causing redness and swelling of the nearby skin.

Symptoms

Symptoms of mast cell tumours in dogs

Many MCT will look like a lump on or just under the skin, but they are infamous amongst vets for having many possible appearances.
Redness and swelling of the skin are common and can develop suddenly.
The size of the lump may increase suddenly or go through phases of being bigger and then smaller.
These lumps are often itchy or tender.
If affecting other organs, symptoms will often involve vomiting, diarrhoea, tarry stools and loss of appetite.
Allergic-type reactions may involve fainting, weakness, swelling of the face, hives and trouble breathing.

Risk

Dogs at higher risk of mast cell tumours

Middle age dogs are most commonly affected, but these tumours can happen at any age.
Several breeds appear to be more commonly affected:
- Boxers
- English and French bulldogs
- Pugs
- Boston terriers
- Labradors
- Golden retrievers
- Rhodesian ridgebacks
- Beagles
- Staffordshire terriers
- Weimaraners
- Shar-peis
- Australian cattle dogs

Diagnosis

Diagnosis of mast cell tumours in dogs

Mast cell tumours can’t be diagnosed based on their appearance, as this can be unpredictable and may even change over time. Two tests can be done, usually with slightly different goals:

Fine needle aspirates are done initially to check if a lump is a mast cell tumour or not
Biopsies will evaluate how aggressive the tumour is likely to be, which helps with treatment decisions

Cases that have additional symptoms or where the tumour may have spread may also benefit from:

Ultrasound scan
Blood tests
CT scan
Biopsy of lymph nodes

Vet treatment

Vet treatment of mast cell tumours in dogs

Surgery is the best treatment when possible. Ideally, this should be done with wide margins around the visible tumour, as it often extends beyond what can be seen.
Radiation therapy can be helpful if surgery is not possible or the biopsy shows there might be tumour cells left after surgery.
An injectable chemotherapy product (Tigilanol tiglate) is now available that can be used in small, superficial MCT in some situations.
Traditional chemotherapy is also an option in some cases.
Medications (Toceranib and Masitinib) are available that can suppress the growth of some of these tumours for extended periods, usually several months.
Other medications that help with the symptoms or prevent complications may be useful, such as antihistamines and antacids.

Home treatment

Home treatment of mast cell tumours in dogs

If a lump becomes red, sore or a wound/crust develops, keep the area clean by bathing with saline (1 tsp salt/500ml cooled boiled water) and speak to a vet as soon as possible. Advice is available in the Joii app 24/7.

Living with mast cell tumours in dogs

Manipulation or damage to a MCT will increase the risk of pain, digestive complications and allergic-type reactions. It is important to avoid:

Self-trauma to the lump (licking or scratching)
Rough handling of the area

Hitting or bumping the lump constantly
- If near joints or areas that rub together during movement, rest is advisable

Mast cell tumours can range from a small, slow-growing lump on the skin to malignant cancer. Some will secrete substances with varying effects on the rest of the body. Because of this, every case will be different and have a different prognosis.

Prevention

Prevention of mast cell tumours in dogs

Unfortunately, there is nothing specific known to prevent the development of mast cell tumours. A healthy lifestyle, with a balanced diet as well as plenty of exercise, is thought to help prevent all types of cancer.

When to worry