Finding a lump, bump, or any irregularity on your pet’s skin can be scary, to say the least. But as soon as you do find anything, it is important to have your veterinarian evaluate it to determine if it is something to be concerned about.
Sometimes lumps and bumps are nothing to be concerned about, but one type of tumor that can occur in your pet’s skin are mast cell tumors, which is a concern.
Our article will help you understand the basics about this type of tumor, so that you can be better informed when making decisions for your pet.
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What Is A Mast Cell Tumor?
Mast cell tumors are comprised of mast cells, hence the name and these cells are a type of granulated white blood cell that play a part in the body’s response to allergens and inflammation.
Mast cells release chemicals and compounds when they are exposed to an allergen. Histamine is one of the compounds released and is responsible for the common symptoms of allergies such as itching, sneezing, runny eyes, and runny nose.
Mast cell tumors are the most common malignant skin tumor in dogs and the second most common in cats.
While mast cell tumors are typically noticed on the skin, they can occur in other parts of the body such as the spleen, intestines, bone marrow, or liver.
Dogs
- Most common skin tumor
- Of skin cancer tumors in dogs, it represents about 16 to 21 % of them.
- While most dogs with mast cell tumors have only one, in 11 to 14 % of cases, multiple skin nodules may be present.
- Low prevalence for other locations (e.g., represent only 0.7% of splenic tumors, and in general, intestinal tumors overall are rare in dogs)
Common locations for mast cell tumors on dogs include:
- Trunk and perineum – 42% to 65%
- Limbs – 22% to 43%
- Head and neck – 10% to 14%
The most common location for cutaneous mast cell tumors in cats is the head (approximately 50%) and neck, trunk (35%) and limbs (12%). The most common site in younger cats was the head whereas in older cats it was the trunk.
Cats
- Most common splenic tumor
- Second most common skin tumor
- Third most common intestinal tumor
Common locations for mast cell tumors on cats include:
The most common location for mast cell tumors on the skin (cutaneous) in cats is the head (approximately 50%) and neck, trunk (35%), and limbs (12%). The most common site in younger cats was the head whereas in older cats it was the trunk.
What Causes Mast Cell Tumor in Pets?
While the exact singular cause is unknown, as with many cancers, it appears that the development of mast cell tumors is, in part, the result of several genetic mutations.
The KIT gene is the most well-known mutation noted in dogs with mast cell tumors.
This mutation is also noted in cats in 56% to 68% of cutaneous (on the skin) and splenic mast cell tumors.
The gender of the dog or cat does not appear to be a predisposition to mast cell tumors.
The average age of dogs diagnosed with mast cell tumors is between 7.5 to 9 years of age. However, dogs of any age can be affected, even those as young as 4 months of age.
In cats, the average age of diagnosis is 10 years or older, but they can develop in younger cats as well. One study stated affected cats were between 6 and 19 years of age.
Breeds Pre-Disposed to Mast Cell Tumors
Any dog or cat breed can develop mast cell tumors but there appears to be some breed disposition in the following breeds:
Dog Breeds
- Beagle
- Boston Terrier
- Boxer
- Bull Terrier
- Bullmastiff
- Cocker Spaniel
- Dachshund
- English Bulldog
- Fox Terrier
- French Bulldog
- Golden Retriever
- Labrador Retriever (Note: Research indicates that the genetic factor that increases the likelihood of mast cell development is carried by 70% of Labrador retrievers and golden retrievers.)
- Pug
- Rhodesian Ridgeback
- Schnauzer
- Shar-pei (Note: They tend to develop them at an early age, and they are often aggressive high-grade tumors.)
- Staffordshire Terrier
- Weimaraner
Cat Breeds
- Siamese
- Burmese
- Ragdoll
- Russian Blue
Signs of Mast Cell Tumors
The signs of a mast cell tumor vary based on its location, such as skin versus spleen, its grade (discussed below), and how long it has been present.
Dog Symptoms
Mast cell tumors on a dog’s skin will vary from small and freely moveable in the skin or just under the skin to large, red, swollen, ulcerated, and hairless tumors. The latter typically occurs when the tumor is more aggressive.
Some grow gradually while others may suddenly appear and grow quite rapidly.
Their size can fluctuate, appearing smaller or larger. This occurs when mast cells degranulate, releasing chemicals and compounds, such as histamine, proteolytic enzymes, and vasodilatory substances, that cause the surrounding tissue to become redden and swollen. These chemicals and compounds can cause problems in other parts of the body when they enter the bloodstream. This can result in the following signs:
- Ulcers in the stomach or intestines
- Vomiting
- Change in appetite
- Lethargy
- Abdominal pain
- Anemia
- Black tarry stool (melena)
- Enlarged lymph nodes
- Anaphylaxis (less common)
Cat Symptoms
The signs noted in cats are based on the location of the mast cell tumor.
Splenic mast cells: Cats are typically sick when mast cell tumors affect this area. You may notice the following:
- Weight loss
- Vomiting
- Loss of appetite
- Enlargement of regional (local) lymph nodes, such as those in the abdomen and chest
Cutaneous mast cells: Their appearance in the skin can vary and generally cats have no other signs other than the tumor. The tumor can be within or below the skin. It can be hard and flattened or a raised red or white bump. It can also appear red, ulcerated, bleeding, bruised, or swollen masses. The growth can remain the same for months or years or it may grow rapidly over days and weeks.
Intestinal mast cell tumors: As with splenic tumors, cats often exhibit signs of being sick. Signs noted are generally dependent on the severity of the disease and include:
- Vomiting
- Diarrhea
- Bloody (fresh and red) stool
- Black tarry stool
- Enlargement of regional (local) lymph nodes, such as those in the abdomen or inguinal (groin)
NOTE: To help avoid degranulation of the mast cells (the releasing of chemicals and compounds in the tumor), you should avoid handling your pet’s tumor. Additionally, prevent your pet from licking, chewing, scratching, or rubbing it.
How a Mast Cell Tumor Is Diagnosed
Any lump, bump, or skin irregularity should be evaluated by a veterinarian to determine if it is a mast cell tumor or any other type of skin tumor since they can resemble warts, bug bites, or allergic reactions.
A fine-needle aspirate (FNA) is the typical way a mast cell tumor is diagnosed. The process involves inserting a small needle with a syringe into the tumor. Then a sample of the cells is suctioned from the tumor. The sample is placed on a microscopic slide, dried, stained with special dyes, and then evaluated under a microscope.
For mast cell tumors located internally, such as in the spleen or intestines, diagnosis is more challenging and may involve an ultrasound or CAT scan. But since many tumors can look similar, to confirm a diagnosis an FNA may be done but it is more invasive as compared to sampling a skin tumor. In some cases, however, a diagnosis can only be made with surgical removal of the mass.
Once it is confirmed that a mast cell tumor is present, further diagnostic testing is necessary in order to determine what other areas of the body are affected as well as aid in grading the cancer. Additional testing can involve a FNA of local lymph nodes, chest X-rays, abdominal ultrasound, and possibly a bone marrow aspirate.
An assessment of your pet’s overall health is also critical so your veterinarian will recommend a complete blood count (CBC), blood chemistry, and urinalysis.
On average, the cost for the initial diagnosis of cancer is between $1,000 and $2,000. However, it can be higher depending on where you live.
Evaluating and Grading the Tumor
A sample of the removed tumor is sent to a pathologist to determine the grade of the tumor and if the surgical margins are free of cancer cells.
The grade is based on the aggressiveness of the tumor. Tumors are graded I to III. The higher the grade, the more aggressive the tumor and the higher the tendency of it to spread to other parts of the body.
The grade as well as the surgical margins will determine if additional surgery, radiation, and/or chemotherapy is needed.
Treating Mast Cell Tumors
The good news is that there are several treatment options available for mast cell tumors. Treatment will be based on different factors such as the location, size, and grade of the tumor.
In addition to the treatments below, your pet may also be given supportive care medications such as steroids, anti-histamines, antacids, anti-nausea, and anti-diarrheal.
Surgery
After diagnosis, the next phase of the process is the surgical removal of the skin tumor. Since mast cell tumors can spread into the surrounding tissue, wide surgical margins are essential to be sure all cancer cells are removed. So even if the mass is as small as a dime, a large area of tissue will be removed.
Manipulation of a mast cell tumor can cause the release of histamine and other compounds. Therefore, your veterinarian may recommend medical management, such as steroids, antihistamines, or histamine blockers, prior to surgery to decrease inflammation and prevent potential side effects.
Low-grade tumors, with no evidence of spreading, are treated via surgery and generally don’t require chemotherapy, especially if adequate margins are obtained. However, close monitoring for regrowth is essential.
In cases where the tumor is large or high-grade, surgery in combination with another treatment option may be necessary.
In cases where the tumor was not completely excised during the first surgical procedure, a second surgery may be recommended.
If surgery is not a viable option, then radiation (described below) may be the next viable treatment option.
Due to the variability in size, location, and grade. On average, expect about $500 to $1,000 for the initial surgical procedure for removal of a mast cell tumor in the skin. But it can potentially be in the range of $4,500 to $7,000 in some cases.
For after-surgery care check out these resources to help keep your pet comfortable and recover well.
After-surgery for dogs
After surgery for cats
Chemotherapy
Chemotherapy is recommended often in combination with surgery, for high-grade tumors even without evidence of spreading, tumors that have spread, or incompletely removed tumors.
It is used in cases where the primary tumor is present within the spleen or intestines.
Per treatment, chemotherapy can range from $150 to $500 per dose. However, in some areas, the price can range upwards of $700 per treatment. How many doses your pet will need is dependent on the type of chemo used and the grade of the tumor. Total treatment costs can exceed $10,000.
Radiation Therapy (conventional fractional)
Radiation can be part of the treatment protocol in cases where the initial surgical margins were not clean (contained cancer cells) and a second surgery is not feasible, or where the tumor cannot be removed surgically.
Radiation can also be used to shrink the tumor to an operable size.
The average cost range for radiation therapy, which is dependent on the tumor grade, size, and location is between $4,000 to $10,000. For conventional radiation therapy, pets typically have between 15 to 21 sessions.
Stereotactic Radiation
This is a ‘newer’ form of radiation used for the same reasons as conventional radiation. Some differences include:
- Maximizes tumor damage but minimally damages surrounding tissue
- Fewer treatments
- Little to no side effects, so recovery is faster
- Possible treatment option for tumors previously considered untreatable
The average cost is about $6,000 to $10,000. For stereotactic radiation, pets have between 1 and 3 sessions.
Receptor Tyrosine Kinase Inhibition
This form of treatment is approved for use in dogs and further research is being conducted to determine its use in cats.
It is used as a treatment option for mast cell tumors that are located within or just under the skin, with no evidence of spreading, are less than or equal to 10 cm in volume, and where injection is possible. The goal is tumor destruction, and a wound is left where the mast cell tumor once was. In some cases, the wound can be extensive and require additional treatment.
The medication is injected directly into the tumor where it breaks down the cancer cells and starves them of a blood supply. A wound or ‘pocket,’ which will require follow-up care, is left where the tumor once was.
With one injection about 75% of tumors respond and with 2 injections, 87% respond. One year after treatment via this method, 90% of dogs were tumor-free.
The average cost is about $500 (range of $450 to $600) per injection.
Palliative Therapy
In cases where the mast cell tumor is not treatable, medications such as painkillers and antihistamines, are used to provide a quality of life.
What Is the Prognosis If Your Pet Has a Mast Cell Tumor?
The prognosis is variable since each pet is unique. It is based on the grade of the tumor, where it is located, and if it has spread.
As mentioned, the higher the grade the more aggressive the tumor. Therefore, the prognosis for a lower-grade tumor is better than that of a higher-grade.
Dogs
Grade I mast cell tumors in the skin are successfully treated with surgery alone in nearly 95% of cases and dogs can live 2 to 4 years or more.
If treatment (surgery, radiation, and chemotherapy) is received, the prognosis is good for pets where the mast cell tumor has spread to local lymph nodes. There are reports of survival times over 5 years.
The prognosis is less favorable for mast cell tumors located where the skin and mucous membranes meet, such as the gums or genital areas.
The average survival time of dogs with Grade III mast cell tumors is 108 days and 16% live up to a year.
The prognosis is less favorable when the mast cell tumor has spread to other tissues or organs.
The prognosis is guarded (not positive) when the tumor is located within the spleen, gastrointestinal tract, or liver.
Cats
The prognosis is good for cats with solitary skin mast cell tumors.
On average, cats live about a year (range of 0 to 739 days) when diagnosed with aggressive mast cell tumors of the skin.
Long-term survival is possible for cats with splenic mast cell tumors following splenectomy alone.
Since metastasis (spreading to other organs or tissue) is common, the prognosis for intestinal mast cell tumors is poor. With aggressive treatment, cats can have a survival rate of 1 to 2 years.
I want to stress that early detection is the key to successful care.
The moment you notice any skin irregularity or change in your pet’s health, have them evaluated by their veterinarian.
As part of your dog’s senior screening, starting at 7 years of age (4 years of age for dogs predisposed to cancer), consider Nu.Q® Vet Cancer Test. This affordable test helps in the early detection of certain cancers and provides you with peace of mind.
