Approved by Sara Ochoa, DVM
July 2, 2022
The life expectancy of a dog with a mast cell tumor depends on the stage and grade of the tumor, the location, treatment options chosen, the particular strain of mast cell tumor and the overall health of the dog.
Most mast cell tumors can be treated with surgical removal without a recurrence.
It’s important to note that very aggressive tumors (considered Grade 3) are also the least common.
The life expectancy of a dog with an aggressive tumor that has spread to other parts of the body (mediatized) is roughly 4 to 6 months.
Assuming the mast cell is in a place where it can be completely removed through surgery (including a wide margin to account for cancer cells not seen) *there is a 90 – 100% chance the tumor will not recur.
[*Source: Long Island Veterinarian Specialists]
What is a Mast Cell?
Canine mast cell tumors (also known as mastocytomas) are common skin tumors in dogs.
Mast cells are actually an important part of a dog’s immune system. These cells aid in the defense against things like:
- parasitic infections
- tissue repair
- forms new blood vessels
- allergic reactions
- non-allergic skin disease
- helps heal wounds
- helps remodel tissue
When mast cells (which are located in the skin, respiratory tract and digestive tract) replicate in abnormal numbers, the result can be a mast cell tumor. Individual mast cell tumors can all look different from one another.
Their shape, size, and appearance isn’t uniform or predictable. That’s why it’s important for a veterinarian to perform diagnostic tests.
In addition, it’s a good reminder not to jump to conclusions if you’ve noticed a lump on your dog. It could literally be anything from a benign tumor to something more worrisome. The only way to know for sure is by seeing a veterinarian.
Diagnosing Mast Cell Tumors in Dogs
Diagnosing mast cell tumors in dogs quickly is essential for a good prognosis. Bring your dog to a licensed veterinarian as soon as you discover a new lump or bump.
The veterinarian may do a series of tests to get an accurate diagnosis including the following:
Fine Needle Aspiration
The first step is to obtain a fine-needle aspiration which will help determine whether the mass is cancerous or not.
Fine-needle aspirations and biopsies are two different things.
The fine-needle aspirate involves inserting a needle into the mass and withdrawing cells for examination. A biopsy, however, involves the removal of a small piece of mass for microscopic examination.
A blood test should be conducted to obtain a complete white blood cell count. A serum chemistry panel and urinalysis help to determine the dog’s overall health condition.
If underlying conditions are diagnosed it can affect the type of treatment options chosen and could affect the dog’s overall life expectancy.
A piece of the tissue is drawn out with a very fine needle and that tissue is examined under a microscope.
The importance of the biopsy is to establish grading of the tumor. Grading of tumors is generally done by a pathologist.
Lymph Node Examination
The veterinarian might feel for enlarged lymph nodes close to the mast cell tumor site.
The examination is painless and can give the doctor a better sense of whether the cancer has spread. If the local lymph nodes are enlarged, a lymph node aspiration may be conducted.
When tumors are found in areas that make it difficult to remove completely through surgery, more tests might be required.
The additional tests help to determine what the treatment options should be.
Abdominal Ultrasound (Sonograph)
Ultrasounds use sound waves to create images of organs within the body. Abdominal ultrasounds are another way to help determine whether cancer has spread to the liver, spleen, and lymph nodes located in the abdomen.
Although radiographs are not entirely helpful in determining the spread of mast cell tumors, they can be useful if there are other underlying conditions present.
Bone Marrow Aspiration
Bone marrow aspiration in dogs involves administering a sedative along with local anesthesia. A needle is then inserted into the bone marrow to remove cells for microscopic examination.
A bone marrow biopsy is more involved and requires general anesthesia. A veterinary surgeon then removes what’s known as a “core sample” of the bone marrow.
Not every dog will require this diagnostic tool.
The “c-Kit” is a molecular receptor found on the surface of mast cells. According to a report by Animal Specialty & Emergency Center, several studies have suggested the presence of mutations in this receptor.
The presence of mutations in this molecular receptor suggests more frequent mast cell tumor recurrence. This test can be done with special tissue analysis.
Grading Mast Cell Tumors
A grading system is used to determine how a tumor might behave (whether it will remain localized or whether it may spread). Tumors can be graded once it has been biopsied.
A pathologist will determine the grade based on its location, signs of inflammation, differentiation of cells.
Grade 1 Mast Cell Tumor in Dogs
Typically benign or non-cancerous. Cells are well-differentiated and have a 25% recurrence rate. There is a low chance that this type of tumor will spread to internal organs.
The life expectancy of a dog with mast cell tumors is greater when the tumor is low grade.
NOTE: The term “differentiated” refers to how much or how little the tumor tissue looks like the normal tissue it came from. The more differentiated mast cell tumors are, the better the prognosis.
Grade 2 Mast Cell Tumor in Dogs
There is a possibility that the tumor is cancerous and may invade nearby skin tissue. These tumors are moderately differentiated and have a 44% chance of recurrence.
When tumors are diagnosed as Grade 2, there is the potential that it could spread or metastasize.
Grade 3 Mast Cell Tumor in Dogs
Grade III tumors represents a more aggressive tumor likely to have spread to other parts of the body. Mast cell tumors at Grade 3 are poorly differentiated and have a high recurrence rate of 76%.
Unfortunately, there is a high risk of the tumor invading internal organs.
Staging Mast Cell Tumors in Dogs
Staging is another step that identifies the extent to which the tumor has spread (or not).
Stage 1 Mast Cell Tumor in Dogs
A stage 1 tumor refers to a single tumor that hasn’t spread to other parts of the body (metastatis).
Stage 2 Mast Cell Tumor in Dogs
At this stage, there is a single tumor that has spread into surrounding lymph nodes.
Stage 3 Mast Cell Tumor in Dogs
Stage 3 mast cell tumors in dogs are classified as “multiple skin tumors” or a large tumor that has invaded skin tissue. There may be lymph node involvement.
Stage 4 Mast Cell Tumor in Dogs
This stage is tricky because the tumor (or multiple tumors) will have invaded the skin and possibly other internal organs. In this case the lymph nodes are likely involved.
Mast Cell Tumors Symptoms In Dogs
It’s common for dogs to develop lumps and bumps, especially as they age. Unfortunately, it’s impossible to determine whether a lump is cancerous or not just by looking at it.
Unfortunately, mast cell tumors are complicated and may or may not involve the presence of the following signs:
- Lumps that randomly increase and/or decrease in size
- Swollen lymph nodes
- Loss of appetite (inappetence)
- Welts on the skin
- Weight Loss
- Bloody or black stool
- Pain in the abdomen
Top Treatment of Canine Mast Cell Tumors
The first line of treatment for dogs with mast cell tumors is surgery. The goal is to completely remove the tumor by including a safety margin of 1 inch around the site.
Surgery for Dogs with Mast Cell Tumors
Surgical removal is generally the treatment chosen to remove mast cell tumors in dogs. A veterinary oncologist will be able to explain how the surgery will be performed including any risk factors for your dog.
When performing the surgery, a wide margin of tissue is also removed. This is performed to ensure that any cancer cells that have migrated into the surrounding skin tissue is removed.
After surgery, the tissue sample is examined under a microscope by a veterinary pathologist. This is done to ensure all cancer cells were removed.
If it appears that there is still some tumor left behind, then a second surgery or the addition of radiation therapy may be required.
Radiation therapy helps to permanently destroy any microscopic cancer cells. This is when high-energy radiation is used to treat cancer. This tends to be highly effective when used in conjunction with surgery.
Unfortunately, there are some drawbacks.
It’s expensive, may not be available in some geographic locations, and requires the use of general anesthesia over the course of several treatments.
Discuss the risks versus benefits of radiation with the veterinarian.
Chemotherapy is an option for dogs who have aggressive mast cell tumors thought to have spread to the lymph nodes and organs. Traditionally, chemotherapy medications are used to prevent cancer cells from dividing.
Chemotherapy is typically considered for dogs who have a high grade tumor (Grade 3) or who are at a Stage 2 (or higher) in regards to the mast cell tumor.
It’s also used for dogs with multiple mast cell tumors occurring at the same time.
Chemotherapy Before Surgery of Mast Cell Tumors in Dogs
If there is a need to reduce the size of a tumor before surgery, chemotherapy can be helpful.
Chemotherapy Medications Used
Conventional chemotherapy for mast cell tumors include the following:
This injectable chemotherapy medication is used to stop the cancerous cells from dividing and thriving. Without their important structural proteins, the mast cell tumor can’t divide and spread.
This drug is used intravenously directly into the bloodstream. Potential Side effects are the result of reduced white blood cells and can include:
This is an oral chemotherapy medication. It is used to disrupt cellular DNA and altering proteins to prevent cells from building DNA and RNA strands.
This medication will also decrease white blood cells and can affect the dog’s liver.
This is also an oral chemotherapy that can be used. Unfortunately, it can reduce normal blood cell numbers and must be monitored closely.
Prednisone is used in combination with other treatment options and may be useful in shrinking the size of the tumors.
In some cases, it may even create a temporary remission. These corticosteroids are highly effective at protecting the body from histamine and other enzymes released when mast cells degranulate.
It’s thought that Prednisone may be toxic to mast cells and may result in a temporary remission. Side effects of Prednisone use may include:
- increased drinking/thirst
- increased urination
- increased appetite
Long term affects may result in muscle loss, lowered immune response, liver enlargement, and weight gain.
That said, Prednisone is inexpensive and worth looking into.
Purchase Prednisone through
Antihistamines help stabilize mast cell tumors in dogs by de-activating excessive histamine release. When large amounts of histamine are released it triggers local inflammation and swelling around the mast cell tumor.
The release of histamine from a mast cell tumor can affect heart rate, blood pressure, and other bodily functions. To counter these effects, antihistamines such as diphenhydramine and hydroxyzine are administered.
Controlling the effects of histamine release are crucial to maintain a dog’s quality of life. Otherwise, the dog may suffer from severe digestive tract symptoms.
Newer Targeted Chemotherapy Medications for Dogs with Mast Cell Tumors
There are now more targeted chemotherapy medications that are available to dogs with mast cell tumors. They are known as:
Palladia (toceranib) by Zoetis
This drug works by killing tumor cells and by cutting off blood supply to the tumor.
Kinavet (masitinib) by AB Science
This drug has been available in Europe (Masivet) and is used to inhibit molecular targets. This drug was evaluated in a clinical trial involving 202 dogs with mast cell tumors.
Random dogs were chosen to receive a placebo or the active drug. The result found was that it took up to 6 months for tumors to progress compared to 2.5 months for dogs treated with a placebo.
Common Side-Effects of Chemotherapy
Dogs typically receive lower doses of chemotherapy than humans. As a result, the side-effects tend to be milder.
Dogs do not lose their fur as a result of chemotherapy, although they may experience appetite loss, vomiting or diarrhea.
Dogs tend to respond very well to chemotherapy with few side-effects. However, if you notice anything unusual or ongoing, be sure to discuss with the veterinarian or veterinarian oncologist.
The Life Expectancy of a Dog With Mast Cell Tumors
Life expectancy of a dog with mast cell tumors really depends on a number of things including the age of your dog, the stage and grade of the tumor, the location of the tumor, and whether the tumor has spread to internal organs.
Naturally, successful treatment relies on the complete removal of the tumor including a wide-margin around it in case cells have begun to spread.
Early diagnosis is better, but it’s not always the key factor in life expectancy.
The good news is that mast cell tumors tend to respond well to treatment. Ultimately, the tumor grade is the most consistent prognosis factor. The more aggressive the tumor (Grade 3 to Grade 4) the worse the prognosis.
Sadly, many dogs living with aggressive tumors pass away anywhere from 4 to 6 months after surgery. This is usually the result of an aggressive tumor that has spread throughout the body.
Prognosis isn’t a template
Dogs with mast cell tumors vary in health. Dogs can be diagnosed at 8 years of age, but sometimes young puppies can be diagnosed. What we’re talking about here is a generalization of dogs with mast cell tumors.
Your veterinarian will be able to give you more distinct guidelines and expectations regarding life expectancy.
Tricky Mast Cell Tumor Locations
It seems that the mast cell tumors that show up in the nail bed, muzzle or oral cavity tend to be more aggressive. In addition, dogs with mast cell tumors in internal organs face a worse prognosis than when the tumor is found in the skin.
Get A Second Opinion
It’s easy to forget to ask certain questions at your regular veterinarian appointment. There may be times when you read a post like this and wonder if it’s accurate!
If you find yourself losing sleep over questions you have about your dog’s health, why not connect with a vet through Chewy.com?
The service is free for individuals who have an autoship membership. Don’t worry though. The cost is still pretty low even if you don’t have autoship.
All you need to do is set up an account and you’ll be on your way!
What Kinds of Questions Can I Ask a Vet Online?
Online veterinarians can’t make a diagnosis. They can, however, offer things like:
- dietary advice for dogs with special needs
- observations on whether medications may need to be tweaked
- advice on what to expect from your dog post surgery
- suggestions on how to minimize side-effects of medications
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Vigilance & Follow-Up Care
Dog owners who have dogs with mast cell tumors will need to maintain regular check-ups with the veterinarian. This is because mast cell tumors have a tendency to come back. They could come back in the same place, or anywhere else on the body.
It’s important for dog owners to carefully watch their dog for signs of new lumps and bumps. In addition, the veterinarian will set a series of follow-up appointments.
Remember that most mast cell tumors can be completely removed through surgery and often do not recur or spread.
It’s important, however, to be aware of any new lumps and bumps on your dog. Mast cell tumors are common in dogs over the age of 8, although they have occurred in puppies.
Nobody can diagnose a mast cell tumor by appearance alone. Unfortunately, these tumors can look like any number of things. Getting an early diagnosis with treatment offers your dog the best prognosis for long-term life expectancy.
I want to thank you for reading this post and would like to wish you the best of luck. We all love our dogs and we do anything it takes to get them on the road to wellness. This is a difficult time for all dog owners and we want to wish you all the best.
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Informative Guide to Mouth Cancer in Dogs
TMS The Mast Cell Disease Society, Inc.
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