The Stages of Mast Cell Tumors and Life Expectancy [With Pictures]

This article was updated on December 12th, 2022

When you find a new lump on your dog, it’s easy to dismiss it as something harmless. In fact, as a veterinary technician, I often see pet owners take a pass when the veterinarian recommends a biopsy on a lump. Owners don’t usually think it’s necessary to biopsy a lump that has been there for years, especially if they don’t think it’s causing problems for their dog. But avoiding treatment is never a good idea. Lumps can suddenly grow rapidly, causing a host of problems for your dog. And lumps that look benign, (non-cancerous) can be cancerous.

This is the case with mast cell tumors, commonly called “the great pretenders” in veterinary medicine. Mast cell tumors have a reputation for mimicking many (non-cancerous) skin lumps. And because of their inconsistent appearance, they can go unchecked for months or even years, causing a wide range of symptoms for dogs affected by them. Mast cell tumors are one of the most common skin cancers found in dogs. And according to one study, they account for 20% of cancerous tumors. It is important that you pay attention to your dog’s skin, and get any new lumps or bumps examined as soon as possible.

How do mast cell tumors affect dogs?

Mast cell tumors most commonly occur in larger breeds, but they can develop in smaller dogs too. According to one study, “breeds most commonly affected by these tumors are Labrador Retrievers, Boxers, American Staffordshire Terriers, Golden Retrievers, Dachshunds, French bulldogs, and Shar Peis.”

No one knows the exact cause of these tumors, but they are believed to be caused by a combination of environmental, genetic, and hereditary risk factors. The tumors are formed when the white blood cells that are responsible for regulating allergic reactions go haywire and divide rapidly. This over-replication of cells causes tumors to form. The tumors can spread through to the deep layers of the skin and into the bloodstream. Most importantly, if the cancer is not caught early enough, it can spread to your dog’s organs. Once the cancer spreads to the organs, your dog can get very sick and may die.

What do mast cell tumors look like?

Mast cell tumors don’t have the same appearance. In fact, they can look like something as harmless as an allergic reaction, or insect bite. The tumors can vary in shape and size and can appear:

• Small
• Large
• Raised
• Flat
• Ulcerated
• Itchy
• Red, pink, or skin-colored

Pictured right:

Pictured left:

How do I know what grade my dog’s tumor is?

Mast cell tumors are graded in three categories. The grade of a tumor is determined by a pathologist. In order to grade a tumor, it must be biopsied or removed by your veterinarian. The tissue will then be examined by the pathologist under a microscope. The pathologist will count the number of mast cells compared with healthy cells to determine the grade of the tumor.

What are the different grades of mast cell tumors and what do they mean?

Grade 1:

Grade 1 tumors are “well-differentiated”, meaning they have a good number of healthy cells compared with cancer cells. At this grade, your dog may have a small or large lump. It could be hard or soft, and a range of colors. The lump could appear out of nowhere, or it could even shrink and grow from day to day. It is best to start treatment when tumors are still in grade 1, as most tumors caught and treated in this grade will not return.

Grade 2:

Grade 2 tumors are moderately differentiated, meaning they have a moderate amount of mast cells compared with healthy cells. At this grade, your dog may have one or more tumors and they may grow quickly or appear very irritated. These tumors are more likely to have grown into the deeper layers of the skin.

Grade 3:

Grade 3 tumors are poorly differentiated, meaning that when the pathologist looks at the cells under the microscope, they will see mostly mast cells and very few healthy cells. Your dog may be very ill at this stage, with one or more tumors covering the skin. The tumor will probably be ulcerated and irritated. Your dog may also exhibit other symptoms caused by the spread of the cancer. Some symptoms your dog may show are:

• Itchy skin
• Welts
• Vomiting
• Weight loss
• Loss of appetite
• Abdominal pain
• Diarrhea

What is the treatment for my dog’s tumor?

There are many treatment options for dogs with mast cell tumors. The treatment will depend on the stage, grade, and location of your dog’s tumor. Your veterinarian will probably recommend a combination of surgery, medications, and possibly radiation or chemotherapy.

Grade 1:

Dogs with low-grade, stage 1-2 tumors can usually be treated with:

• Surgery
• Antihistamines
• Steroids
• Antacids

The treatment option for Grade 1 tumors is surgical removal. The veterinary surgeon will remove large margins (around 2-3 cm) of healthy skin around the tumor. This will ensure most of the cancer cells are removed. The tissue removed during the surgery will be sent to a pathologist and microscopically examined.

Grade 2:

Dogs with high-grade, stage 2-3 tumors will often require a combination of:

• Surgery
• Chemotherapy
• Radiation
• Antihistamines
• Steroids
• Antacids

Similar to a grade 1 tumor, grade 2 tumors are treated with surgical removal. At this grade, chemotherapy is usually recommended, along with surgery. Because of the high amount of cancer cells present in Grade 2 tumors, there is a higher chance that some cells could be left behind after surgery. Chemotherapy and radiation treatments are used to kill off any of the cancer cells left behind, further decreasing the chances of the tumor growing back.

Grade 3:

Grade 3 mast cells tumors are high-grade tumors. These tumors are so aggressive that your veterinarian will likely recommend surgery, medications, chemotherapy, and radiation. At this grade, surgery may not be an option. If surgery is not an option, your veterinarian will focus on keeping your dog comfortable rather than eliminating the cancer.

How long will my dog live with a mast cell tumor? 

Because every dog with a mast cell tumor is different, it is hard to say how long a specific dog will live. There haven’t been enough studies done yet, but according to current information, your dog’s length of life will depend on:

• The stage of the tumor
• The grade of the tumor
• The location of the tumor
• The number of tumors
• Your dog’s overall health

In a 10-year-long study, results found that out of 149 dogs, 65.1% had no new tumors, no spread of cancer, and no deaths after diagnosis. The same study showed that 30.8% of the 149 dogs passed away within 1020 days of diagnosis.

Life expectancy of dogs with mast cell tumors – by tumor grade

Grade 1 and 2:

Grade 1 and 2 tumors are the easiest to treat. Most dogs with these tumors will fully recover with no tumor regrowth after surgery. Dogs with low-grade tumors will have a good outcome. Many of them only require follow-up exams to make sure no new tumors are growing. If all the cancer cells are removed during the surgery, “90-100% of the time the tumors do not return.” According to a veterinary article, “The prognosis for even incompletely removed grade 1 or 2 tumors treated with radiation after surgery is excellent, with 90-95% of dogs having no reoccurrence of tumor within 3 years of receiving radiation therapy.”

Grade 3:

With surgical removal and chemotherapy, the average life expectancy of a dog with a grade 3 mast cell tumor is 12 months. With surgery alone, about “50% of patients will live to 6 months after tumor removal.”

Will my dog live a normal life with a mast cell tumor?

If your dog is diagnosed with a mast cell tumor, his quality of life will depend on the stage of the cancer and his general health. Many dogs can live life with few complications, especially when the tumor is caught and treated early on.

Quality of life with low-grade tumors:

Luckily, low-grade tumors that are caught early have a good chance of being removed successfully. According to one study, roughly “80% of mast cells are low-to-intermediate grade and unlikely to reoccur after surgery.”

Quality of life with high-grade tumors:

Because high-grade mast cell tumors are the most aggressive, it is very important that these tumors are caught early. These tumors have a higher chance of spreading to the lymph nodes and metastasizing (spreading to other organs in the body.) Once a tumor spreads to the organs, the chance that your dog will live a normal life is very low. Tumors that metastasize will cause a lot of symptoms, so at this grade, the focus of treatment will be on keeping your dog as comfortable as possible.

How will the medications help my dog?

There are many medications that can keep your dog comfortable throughout the treatment process. For instance, antihistamines like Benadryl are used to calm down the allergic response in your dog’s blood, making them less itchy. Prednisone is a steroid that can also help decrease inflammation and itching. Antacids are used to soothe the stomach and decrease the nausea caused by irritation in the stomach.

What if my dog is not a candidate for surgery?

Sometimes a tumor can be too big to remove, or it can be in an area that makes it impossible to perform surgery. In these cases, veterinarians can offer palliative care (comfort care). Palliative care usually includes “4 weekly doses of radiation, followed by a 15-week course of chemotherapy”. A combination of radiation and chemotherapy can decrease tumor size. Additionally, your veterinarian will likely include medications to control symptoms of stomach upset, pain, and itching. Palliative care is for patients that cannot be cured of the cancer. However, it offers improvement in symptoms. The average survival time for patients that receive palliative care is 3 months.

What stage tumor does my dog have?

Mast cell tumors occur in three stages. The stage of the cancer is determined by how much the tumor has spread to other parts of your dog’s body. In order to determine the stage of the tumor, it may be necessary for your veterinarian to collect samples of cells in the lymph nodes near the tumor. Your veterinarian will then send the cell sample to the pathologist to be examined. By determining the stage of the tumor, your veterinarian will decide the type of treatment that is best for your dog.

What can I do to stop my dog’s tumor from growing?

The growth of mast cell tumors cannot be stopped. However, there are many ways to prevent your dog’s tumor from spreading. The treatments for mast cell tumors are varied, and really depend on the characteristics of the tumor. Your veterinarian will look at the following three characteristics when deciding how to treat the tumor:

• Grade
• Stage
• Location

Will chemotherapy make my dog sick?

Both chemotherapy and radiation are tolerated pretty well by most healthy dogs. However, it is important to remember that chemotherapy wouldn’t be used if the benefits didn’t outweigh the risks. Dogs receiving chemotherapy will need to have a full health evaluation before treatment. This will include bloodwork to check for any abnormalities in cell or organ function. Bloodwork is a great way for your veterinarian to determine if your dog is a good candidate for chemotherapy. However, with chemotherapy, there is always a risk of side effects. Some of the side effects seen in dogs undergoing chemotherapy are.

• Vomiting
• Diarrhea
• Dehydration
• Low white blood cell count
• Bladder irritation

What will treatment for my dog’s mast cell tumor cost me?

The cost of treatment for mast cell tumors is variable and depends on several factors. Things like the number of tumors, the size, and location of the tumors, and your geographical location will all affect the cost of surgery. Most tumor removal surgeries can cost anywhere from 500-1,500 dollars or more.

Chemotherapy can cost anywhere from 3000-4,000 dollars. Radiation can also be quite pricey at about 2500-7,000 for 3-6 months of treatment. Prescriptions like antihistamines, steroids and antacids are typically the most affordable part of mast cell tumor treatment, costing typically around 20-50 dollars a month.

How can I get my dog tested for a mast cell tumor?

Tumors can easily be checked by your veterinarian with a procedure called a FNA, or a fine needle aspirate. During this procedure, your veterinarian will insert a small needle into the lump to collect some cells. After collecting the sample, your veterinarian will send it off to a laboratory. At the laboratory, a pathologist will examine the sample for cancerous cells. It usually takes about a week for the results to come back for this type of test.

Takeaway

Overall, there is hope if your dog has a mast cell tumor. The most important thing you can do as a pet owner is have your dog’s new lumps checked by your veterinarian as soon as you notice them. The good news is that tumors caught early are treatable and unlikely to return.

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