Mast Cell Tumours in dogs


  • Mast cell tumours (MCT) are a type of skin cancer in dogs.
  • They can be tricky to spot because they all look different and often grow and shrink in size.
  • MCT’s vary from low-grade (not very aggressive), to high-grade (very aggressive).
  • Surgery to remove low-grade MCT’s can sometimes cure the problem, but high-grade MCT’s have often spread by the time they are diagnosed, and tend to be much more difficult to treat.
  • If your dog has a MCT their outlook will depend how aggressive it is, where it is, if it's spread, and how well it responds to treatment. 
  • Contact your vet if your dog has any new (or changing) lumps.

General information

Mast Cell Tumours (MCT) are a very common type of skin cancer in dogs. They tend to affect middle age dogs, and are especially common in certain breeds such as Boxers and Beagles. MCT’s range from being low-grade (not very aggressive) to high-grade (very aggressive). MCTs can release ‘histamine’, a chemical that causes inflammation.  Which is why they often become swollen, itchy and irritated, and can sometimes cause problems in other parts of the body such as the stomach.

Some dogs will get more than one MCT during their lifetime, so it’s important to get any new lumps checked by your vet, especially if one has appeared quickly, or is red and irritating.


  • Mast cell tumours are skin lumps, they don’t all look the same, and can grow and shrink very quickly.
  • They can be found anywhere on the body, but are most common on the chest, legs, feet, and around the bottom.
  • They are often red, inflamed and itchy.

When to contact your vet

Any new skin lumps on your dog should be checked ASAP, especially if they are red, itchy or growing quickly.

Occasionally, harmless skin lumps can change into something more serious over time so it’s also important to contact your vet if your dog has a benign skin lump that’s changing. You know your pet best, always contact your vet if you are concerned.

Diagnosis and Grading


If your vet suspects a MCT, they will need to confirm the diagnosis by taking a sample and having it analysed (usually at a lab). Samples can usually be taken by needle and syringe in a consult, but sometimes require a sedation or anaesthetic.


MCTs can be graded to show how aggressive they are. This is done at a lab by a specialist who looks at a sample of the MCT under a microscope. Your vet will use the grade of your dog’s MCT to help decide on the type of treatment they need. 

  • Low-grade MCTs tend not to spread, and can often be cured by surgical removal.
  • High-grade masses are more aggressive, spread around the body and affect other organs. If your dog has a high grade MCT, your vet may need to run other tests (such as blood tests, ultrasound scans or x-rays) to see if it’s spread elsewhere in the body.


Treatment for your dog’s mast cell tumour will depend on its location, size, grade, and whether it has spread or not. Some require surgery, some require chemotherapy and a few require radiotherapy. Unfortunately, not all MCT’s are curable.


  • Surgery to remove a low-grade MCT (that hasn’t spread) is sometimes enough to cure the problem.
  • As well as the removing the lump, your vet will need to take some of the skin from around it to make sure all the cancerous cells are removed. This means that the wound from surgery is likely to be much bigger than the lump itself.
  • It’s very important to monitor your dog and their wound closely after their surgery to make sure the stitches holding the wound together don’t break down and it doesn’t become infected.


  • Chemotherapy is often recommended for high-grade MCTs.
  • Your vet might recommend a special type of chemotherapy (for example masitnib and torcerinib) which specifically targets certain types of MCTs.
  • Your vet may recommend surgery before or after chemotherapy depending on the grade of their MCT.
  • Sadly, with high grade MCTs that have already spread, chemotherapy is not always effective.
  • Some chemotherapy drugs used have side effects.
  • Talk to your vet about which treatment is best for your dog especially if you have any questions or concerns.

Other treatments

  • Radiotherapy is sometimes recommended alongside other treatments for some MCT’s, for example if it’s not been possible to completely remove the MCT from your dog’s skin.
  • Some dogs with MCTs benefit from medications such as anti-histamines (because MCTs release histamines) or stomach protectants (because histamines can cause stomach problems).


If your dog has a low grade MCT that can be removed completely, their outlook is good. If they have a high-grade MCT that has spread elsewhere, their outlook is unfortunately much poorer (even with treatment). Dogs can get more than one MCT during their lives so it’s always important to get any new skin lumps checked as soon as possible especially if they have had a MCT in the past.

In some cases, you may need to consider putting your dog to sleep if they are suffering due to symptoms of a MCT.


Treatment for MCT can become very expensive, especially if they need specialist treatment such as a complex surgery, chemotherapy or radiotherapy. It’s important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your pet. There is often more than one treatment option, so if one doesn’t work for you and your pet then the vet may be able to offer another.

When you welcome a new dog into your life, consider getting dog insurance straight away before any signs of illness start. This will give you peace of mind that you have some financial support if they ever get sick. 

Breeds prone to MCT

There are some breeds that seem to be more prone to getting MCT and some of these breeds can get lots of MCTs during their lifetime. These include:

Published: September 2020

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.