Can Dogs Live with Mast Cell Tumors?

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Introduction

The big C word, "cancer", is something no dog owner ever wants to hear. Unfortunately, it's a diagnosis far too many dogs across the nation receive every year, and the disease can take many forms.

The most common form of skin tumor that affects dogs is the dreaded mast cell tumor. This tumor develops in a dog's mast cells as a result of a mutation of those cells, and if malignant can have life-threatening implications.

Finding out that your dog has a mast cell tumor can be devastating and bewildering news, but don't give up hope. There are multiple treatment options available that could potentially give your dog a shot at a bright future, so let's take a closer look at how mast cell tumors work and how you and your pet can fight back against these unwanted growths.

Signs and Symptoms of Mast Cell Tumors in Dogs

Mast cell tumors can vary widely in their shape, appearance, and size. They can be benign in some cases but most are malignant, so it's essential to recognize any warning signs and get your pet checked out by a veterinarian as soon as possible.

Most canine mast cell tumors occur either in the skin (cutaneous) or just underneath the skin (subcutaneous). They can also occur in other parts of the body, including the conjunctiva, the salivary glands, the lining of the mouth and throat, and even the spine, but these only occur occasionally.

The most common symptom that leads to the diagnosis of a mast cell tumor is a lump in the skin. That's right, any skin lump could potentially be a mast cell tumor, so it's important to get it checked by your vet. Some dogs will be diagnosed after a lump that's been there for ages finally gets checked out, while others will present with an angry-looking and rapidly growing lump that needs immediate attention.

The cells of a tumor produce a range of chemicals that affect nearby blood vessels and cells of the immune system. This can make the tumor look like an infection or an inflammatory reaction, so lumps that are red, itchy, bleeding, bruise easily, and are surrounded by swelling should be investigated straight away.

Finally, vomiting and a loss of appetite can also be a sign of mast cell tumors. While these symptoms may seem completely unrelated to the skin, the histamine released from a tumor can cause stomach ulcers, which, in turn, can lead to vomiting.

Body Language

Make sure you pay close attention to your dog's body language to pick up any indications that they may have a mast cell tumor. These could include:
  • Scratching
  • Weakness

Other Signs

Other clinical signs you may notice include:
  • Skin lump
  • Red, angry-looking lump
  • Swelling around the lump
  • Vomiting
  • Loss of appetite

The Science of Mast Cell Tumors in Dogs

Mast cells themselves are normal cells that are found in nearly all organs and tissues of your dog's body. Originating in the bone marrow, they then mature in other tissues, with particular concentrations in the skin, respiratory tract and digestive tract. 

Mast cells play an important role in your dog's immune system, fighting infection and playing a part in allergic reactions. One of the most important features of mast cells is that they produce histamine, which, in the right quantities, is essential for the dog's normal response of inflammation.

However, when mast cells mutate and begin to replicate in higher than normal numbers, mast cell tumors can form. While some of these tumors are benign and can be cured by surgery, others will aggressively spread throughout the body and cause serious health issues. The overproduction of histamine can also cause stomach ulcers, leading to vomiting or black, tarry stools.

If you're wondering why your dog may have been unlucky enough to get a mast cell tumor, the answer is simply that we don't know. While it's not certain what causes this form of cancer, it's likely that there are a variety of contributing factors.

Tumors can affect dogs at any age, and certain breeds are predisposed to developing them. These breeds include the Boston Terrier, Boxer, English Bulldog, Bullmastiff, Labrador, Golden Retriever, and Staffordshire Bull Terrier.

Diagnosis and Treatment of Mast Cell Tumors

After assessing your pet's medical history and conducting a thorough examination, the most important step your veterinarian will rely on to diagnose a mast cell tumor is the examination of cell samples. These samples may be obtained by aspiration or fine needle biopsy, and will help your vet decide on the best course of treatment.

Unfortunately, one of the very few things we can predict about mast cell tumors in dogs is that they're highly unpredictable. The treatment that works best for one dog may not necessarily be the right choice for another, so the focus is on assessing each pet on a case-by-case basis.

However, tumors are usually graded on a scale of I to III:

  • Grade I tumors are considered benign and the prognosis is generally good. Approximately 36% of mast cell tumors are classified in this category.
  • Grade II tumors are the most common, making up approximately 43% of diagnosed cases. More than half of these tumors can be cured by surgical excision, but choosing the best treatment option can be difficult. In recent years, as part of an effort to reduce confusion about the best treatment for Grade II tumors, a new system has been introduced to classify mast cell tumors as either high grade or low grade.
  • Grade III mast cell tumors are aggressive and spread to other areas of the body. They make up roughly 20% of all cases and are treated with chemotherapy.

The treatment and prognosis for your pet varies on a case-by-case basis, so speak to your vet or treating specialist about what you can expect.

Mast Cell Tumor Prognosis:

  • Grade I tumors: If the whole tumor can be removed, the prognosis for dogs with these generally benign tumors is quite good.
  • Grade II tumors: These are the hardest type of mast cell tumors to predict. While some act benignly, a small portion act aggressively - but it's very difficult to forecast which ones will do so. While around two-thirds can be cured surgically, recurrence of the tumor and the spread of cancer to other parts of the body are both possible.
  • Grade III tumors: Usually malignant, Grade III mast cell tumors have a high chance of regrowth after surgery and are highly likely to spread to other parts of the body. Unfortunately, most dogs with this type of tumor will survive less than one year.