Cancer is an extremely common occurrence in dogs, especially as they reach their golden years, but that doesn't mean that every lump and deformation in a dog is a cancerous tumor. Still, approximately 20% of all canine skin tumors are mast cell tumors.
As a vet, it's essential that you know how to identify, diagnose, and treat various kinds of canine cancer, including mast cell tumors. If you don't have that oncology specialty, it can be highly beneficial to keep a remote oncology service like ours on call.
While you consider that, read on to learn more about mast cell tumors, how they present, and what you can expect.
What Are Mast Cells and Mast Cell Tumors?
Mast cells are a kind of cell throughout the body. They're a kind of specialized white blood cell and are often found in connective tissues, particularly in the skin. They're packed full of granules of chemicals that, when they detect an invader in the body (usually an allergen), are released in a process called degranulation.
These chemicals, like histamine and cytokines, are part of the body's immune response. In people, the allergic reaction can involve things like rashes, itching, congestion, and sneezing. Similar effects can impact dogs as well.
Mast cells are usually fine; they're a vital part of the immune system's response to allergens.
Sometimes they go haywire and can cause things like excessive mass degranulation leading to anaphylaxis, a cytokine storm, or even death in extreme cases.
Even when things don't go awry with the immune response, mast cells are still a kind of cell in the body, and every type of cell has the risk of being mutated and turning cancerous.
Mast cell tumors are cancerous mast cells that replicate out of control in a solid mass tumor.
Mast cell tumors are most commonly seen in the skin, though they can also show up in other regions, including in bone marrow, the intestines, or in the liver or spleen.
They are generally isolated, and 60-70% of cases only present one tumor.
Different Types of Mast Cell Tumors in Dogs
Mast cell tumors can be evaluated and categorized based on a few different qualities they may possess.
This gives them a grade, which in turn helps identify both the appropriate treatments and the prognosis.
The first is the kind of tumor out of three. The three categories are cutaneous, subcutaneous, and visceral. All these mean is where the tumor is:
Cutaneous means "in the skin" and means the mast cell tumor is part of the skin itself.
Subcutaneous means "beneath the skin" and means that the tumor is part of the connective tissues and other flesh that makes up the scaffolding wrapping the body.
Visceral means part of the viscera, i.e., the organs. Mast cell tumors in the organs are visceral tumors.
Other aspects of a mast cell tumor can also be evaluated. Fine needle aspiration and a histological panel can help identify the microscopic characteristics of a given tumor and can help grade the tumor.
There are two different grading systems in use with canine mast cell tumors. The older grading system is a three-stage system, where Grade I tumors are the most minor and least aggressive, while Grade III is the largest, most aggressive, or have spread in metastases throughout the patient's body.
The newer grading system is a two-stage system, categorizing tumors as either High Grade or Low Grade.
"High Grade" is the dangerous, aggressive tumors, while "Low Grade" is the calmer, less dangerous tumors.
Warning Signs and Symptoms of Mast Cell Tumors in Dogs
When a dog comes into your clinic with a strange lump, what should you look for to determine whether or not the lump is a tumor or, specifically, a mast cell tumor?
Mast cell tumors can show up anywhere mast cells are present, which is unfortunately everywhere throughout the body. Often, they are raised lumps that are on or just under the skin. They may be swollen, red, or ulcerated, but often they aren't, particularly if they're relatively new or low-grade.
Mast cell tumors are unusual in their presentation. Some will remain static for weeks or months at a time. Others will appear and proliferate, going from nothing to a large, visible tumor in weeks. Some even fluctuate in size, both growing and shrinking, from day to day.
Mast cell tumors may also respond to agitation. Mast cells degranulate upon being stimulated, which causes localized redness and swelling; mast cell tumors can also degranulate if they're the right type of mast cell tumor to retain the capability. This means that a pet owner poking and prodding a tumor can make it swell, and it can swell and look worse in response to aspiration.
Mast cell tumors degranulating can also cause problems throughout the rest of the body. These problems can include symptoms like stomach ulcers, lethargy, loss of appetite, and internal bleeding in the digestive tract.
In rare cases, anaphylaxis and other more dangerous reactions can occur.
Mast cell tumors are common in dogs, but certain breeds are more likely to get them than others.
Labradors, Bull Terriers, Boston Terriers, and Boxers are all more susceptible. Pugs are also at high risk and are more likely than other breeds to have multiple mast cell tumors.
Diagnostic Techniques for Mast Cell Tumors in Dogs
With most lesions and lumps, the first line of diagnostics is a simple fine needle aspiration.
With this, a needle is used to extract cells from the tumor, which are then examined under a microscope. An example of what mast cell tumors might look like can be seen here:
Another example, without granules characteristic of mast cell tumors, is this:
Of course, if you don't have the oncology training to know what you're looking at here and how they differ from normal cells or even normal mast cells, these pictures don't give you much.
In that case, your best option is to have an oncologist or tumor pathologist on call. A simple solution to this problem is to keep us on your contact list.
Mast cell tumors are often complex to diagnose initially. Because of the wide range of appearances of the tumor on the surface, they are often misidentified as other less aggressive or dangerous tumors, as cysts, or even as insect bites. On top of that, because they stem from allergic cells, they can be misidentified as allergic reactions.
In cases where a mast cell tumor requires more accurate diagnosis and staging to prepare an appropriate treatment, a biopsy may be conducted as well. A biopsy is essentially just like a needle aspiration, but larger; taking a larger sample of the tumor to send to pathology and even genetic testing to identify specific details of the tumor for more accurate treatment.
The progression of mast cell tumors in dogs can be challenging to predict. Because of the vast array of symptoms and stimuli involved in mast cell tumors, they can present themselves in a lot of different ways. Some dog breeds are more predisposed to developing MCTs than others. MCTs can occur at any age, but they are more commonly found in middle-aged to older dogs. Tumors located on the limbs, head, or neck may be more difficult to remove surgically due to the surrounding anatomy, potentially leading to incomplete removal or higher chances of recurrence.
Various factors will be considered, including the dog's breed and age, the location of the tumor (tumors near the junction with mucous membranes, like in the gums, are often worse), the grade, the stage, existing treatments, and how actively the cells are replicating - each of these things can affect the prognosis.
Treatment Options for Mast Cell Tumors
Treatment for mast cell tumors varies depending on the grade and staging of the tumor, the size, and aggressiveness of the tumor, the results of a prognostic panel and genetic testing, and other factors.
The good news is that mast cell tumors are among the most treatable of all canine cancers. This is due in part to the fact that the majority of them are localized to one single tumor, and they can often be slow-growing or even dormant for long periods of time.
The first step of treatment is a full inspection, including imagery of the dog in question, to check for any secondary tumors or metastases. These vastly complicate the situation and reduce the likelihood of positive outcomes.
With low-grade tumors that are themselves isolated and individual, a simple surgery is the easiest way to remove and treat the tumor. However, sometimes the scope, scale, location, or staging of the tumor means that surgery alone won't be able to do the job.
In these cases, more comprehensive treatment will be required. Often, chemotherapy is the next step. Radiation therapy is possible in cases where the tumor is located such that it can't be surgically removed.
Another possible treatment is the medication STELFONTA, known generically as "tigilanol tiglate." This is an injection that is delivered directly to the tumor, where it cuts off the blood supply and directly attacks and breaks down the tumor cells. The tumor will essentially shrivel up and die, fall off, and leave an open wound that can be treated just like any other open wound.
Other medications help control the side effects of STELFONTA, including antihistamines to mitigate the impact of the mast cells degranulating as they die, antacids to prevent stomach ulcers, and prednisone, which helps stimulate the patient's body into healing. But, all of those are much less harsh on the body than chemotherapy drugs, making it a great tool in any vet's arsenal.
Pictures of Mast Cell Tumors and Treatment
Below, we have two examples of successful uses of STELFONTA on patients.
First up is Missy.
Here you can see the ease of injection and the progress of the tumor's death and subsequent wound.
After seven days, a wound has opened on the patient's leg, and the tumor is in the process of dying.
After 14 days, the wound was fully open, and the tumor was essentially gone.
After 30 days, the wound has reduced in size by half and is well in the process of healing.
The Second is Murphy.
Murphy's wound has opened up a mere four days after injection, and by 11 days later, it has reached about the largest size it gets.
By 33 days, it has healed down to the size of a dime.
By 49 days, it is almost completely healed, with only a tiny scab and path where fur has yet to regrow, remaining to show a tumor was ever there.
These are examples of relatively easy treatment of a mast cell tumor; they're close to the surface, on a limb, and don't require surgical removal, chemotherapy, or radiation.
Management and Follow-Up Care for Dogs with Mast Cell Tumors
In almost all cases, mast cell tumors are relatively easily treatable. Only in advanced cases with high-grade tumors are systemic treatments like chemotherapy, radiation, and pred all recommended.
In any case, once the tumor is gone, follow-up care is simple. For something like STELFONTA, the patient will be seen frequently to monitor the progression of the medication and to determine whether or not a second injection will be necessary. Once the tumor is gone, all that remains is proper wound care to prevent infection.
Long-term follow-up is the same as any vet visit; checking for reoccurrence of disease, which is rare, and for other health problems which can crop up in patients. Properly treated mast cell tumors don't frequently come back, but higher-grade tumors do, which is why it's important to catch and treat these tumors as early as possible.
Risk Reduction and Prevention of Mast Cell Tumors in Dogs
Cancer is a tricky disease because it's such a wide range of different diseases of different kinds of cells, and there are a vast array of varying risk factors. Genetics, exposure to radiation sources, and even cosmic rays that are untraceable and unpredictable can all be contributing factors.
As such, there's not much anyone can do to prevent cancer from forming. The best option is for patients to see their vets on a regular basis and to get any irregular lumps or other tumors diagnosed as soon as possible.
If your practice is overwhelmed, as so many are today, by high volumes of patients and increasingly complex situations involving emergency medicine, internal medicine, cancers, neurology, or dermatology, we're here to help. You don't need to be a specialist in everything when you have specialists on call for immediate consults. Just reach out today and discuss what we can do for you.