Treating Mast Cell Tumors in Dogs

Atlantic Veterinary Internal Medicine & Oncology offers state-of-the-art treatment options for dogs with mast cell tumors at its Annapolis, Columbia, and Towson animal hospitals. 

Mast cells are special blood cells that are normally involved in the body’s response to allergens and inflammation. When these cells mutate, they develop into a mast cell tumor. Mast cell tumors are commonly found on the skin, but other sites include the lymph nodes, spleen, liver, bone marrow, and intestines. Mast cell tumors are often raised, red, hairless masses that can wax and wane in size.

Mast cells contain substances within their granules (the most common ones are histamine and heparin) that can cause local inflammation (redness) and occasionally bleeding. Due to the effects of the granules, most patients will be started on anti-histamines and antacids for supportive care.

Treating Mast Cell Tumors in Dogs: A Mast Cell Tumor on the Stomach of a Dog

Any new lump or bump should be evaluated by your veterinarian. There are several breeds that are at a higher risk of developing mast cell tumors in their lifetime, including Boxers, Bulldogs, Pit Bulls, Pugs and Boston Terriers, but dogs of any breed can be diagnosed with a mast cell tumor.

Treating Mast Cell Tumors in Dogs: A Microscope Image of Mast Cells


A mast cell tumor is usually diagnosed by fine needle aspiration. This procedure entails inserting a needle into the mass and aspirating back some cells. The cells that are removed are put on a slide and sent out to the laboratory for the pathologist to review.

Mast cell tumors vary in behavior. Some are slow-growing and less aggressive, while others grow quickly and cause discomfort. Initial evaluation of a dog with a mast cell tumor usually involves additional diagnostics to determine the extent of disease (also known as staging the disease). The most common sites for metastasis are the draining lymph nodes, liver, spleen, and bone marrow.

Additional diagnostics include:

  • Bloodwork (complete blood count and chemistry panel)
  • Urinalysis
  • Chest X-rays
  • Regional lymph node aspiration
  • Abdominal ultrasound to evaluate the liver, spleen and lymph nodes
  • Possible aspiration of the spleen

In some cases, we may also recommend a bone marrow aspirate. There are additional tests that can be done to try and predict the behavior of the mast cell tumor. This can include testing for a mutation, called c-kit, or performing a mast cell tumor panel.

Mast cell tumors are graded in two ways:

  1. Patnaik scale: Tumors are graded I-III. Grade I tumors are the least aggressive, Grade II tumors are the most common, and Grade III tumors are the most aggressive.
  2. Two Tier Scale: Tumors are graded high or low. Low-grade mast cell tumors are considered locally aggressive. High-grade mast cell tumors are not only locally aggressive, but are likely to spread to other areas of the body.

Treating Mast Cell Tumors

Treatment options for cutaneous mast cell tumors may include surgery, radiation therapy, chemotherapy and/or supportive care.

The gold standard of treatment is surgery to remove the mass. Mast cell tumors can be invasive and therefore, the surgeon will want to be aggressive by taking a large margin both around and under the tumor to try and ensure complete removal. Unfortunately, even when a large margin is taken, some of the tumor cells can still be left behind. When a mast cell tumor is not completely removed, there is a concern that there will be recurrence along the scar. If incomplete margins are found, then additional surgery or radiation therapy may be needed.

The goal of radiation is to try and clean up the residual disease that remains to slow the recurrence rate. Fortunately, radiation is very effective at preventing/slowing local mast cell tumor recurrence. Radiation therapy is administered while the patient is under anesthesia and consists of a daily treatment, Monday through Friday, for 3-4 weeks in a row. Studies indicate local control times of 2-5 years for patients treated with surgery and radiation.

Surgery and radiation therapy are local treatments that do not affect the spread of the tumor. Chemotherapy is beneficial for patients with a mast cell tumor that has already spread, is too large for surgery, or when there is a high risk for metastasis. Chemotherapy can be used with surgery or alone, but it is much more effective if the tumor has been removed.

Fortunately, chemotherapy is well-tolerated by most patients. Side effects may include stomach upset, a decreased white blood cell count, and possible thinning of the fur coat. Fewer than 10% of patients treated will experience significant side effects that warrant a visit to the animal hospital for outpatient care, and less than 1% will experience any life-threatening side effects or need to be hospitalized.

The prognosis for cutaneous mast cell tumors depends on the grade of the tumor, its location, whether or not it is positive for the kit mutation, and the presence of metastasis. Once a patient develops a mast cell tumor, they are at risk for developing others in the future. The majority of mast cell tumors can be successfully treated when found early.

The goal of any treatment option is to help maintain a good quality of life for your pet for as long as we can. Your oncologist will be able to discuss the treatment options available and what is best for your pet.

Understanding Bladder Cancer in Dogs

Happy dog: Bladder Cancer in dogs in Annapolis

Our canine companions are just as likely to get cancer as humans are, and bladder cancer is one such type. The tumor that affects the bladder is known as transitional cell carcinoma, or urothelial carcinoma. It’s the most common tumor diagnosed in the bladder, and is diagnosed in roughly 80,000 dogs every year. The breeds affected most include Beagles, Scottish Terriers, Border Collies, and Shelties.

Common Clinical Signs

The most common signs indicating bladder cancer are:

  • Urine accidents in the house
  • Straining to urinate
  • Urinating more often
  • Blood in the urine
  • Urgency to urinate, but unable to produce much urine

Other health problems can cause these symptoms. However, with bladder cancer, the symptoms may be resolved for a short time with symptomatic therapy and then return not long after your pet has discontinued their treatment.

Diagnosing Bladder Cancer

  • CADET® BRAF – The first test we would choose for diagnosing transitional cell carcinoma (TCC) is the non-invasive CADET® BRAF test. ‘BRAF’ is the name for a gene that, in affected dogs, contains a single mutation indicating TCC. All we need to do is collect 30-40ml of your dog’s urine (over several days) and have it evaluated in a laboratory.
  • Cystoscopy – If the first option produces inconclusive results, we can try cystoscopy. A flexible scope is carefully inserted through the urethra and into the bladder while your pet is under anesthesia. We can then examine the urethra and bladder and take tissue samples for biopsy.
  • Urine cytology  – Urine cytology is a third option where we can examine cells that have been shed into the urine. We can make a correct diagnosis with this test about 30% of the time.
Small dog sitting outside: Bladder Cancer in dogs in Annapolis

Bladder Cancer Staging

Following a definitive diagnosis, we need to determine whether your pet’s cancer has spread into the lymph nodes, bones, and/or lungs. Therefore, before starting treatment, we need to perform:

  • Blood work and urine testing
  • An abdominal ultrasound to view the bladder, urethra, kidneys, regional lymph nodes, and abdominal cavity overall)
  • Chest X-rays and/or a CT scan to check for TCC within the lungs
  • A rectal exam to check for an enlarged prostate, lymph nodes, and urethra

Treatment Options for Pets

The goal of treatment is to slow cancer progression and improve your pet’s quality of life as much as possible. Available treatments include:

  • Piroxicam, an oral NSAID that decreases inflammation around tumors and helps to improve or resolve clinical signs. It has been found to have slowed tumor growth in approximately 18% of pets.
  • Chemotherapy, which can be used together with Piroxicam to treat TCC. Chemotherapy does not cause the same dramatic side effects in pets as it does in humans.
  • Radiation therapy is also a possible option and can be performed while your pet is under anesthesia.

We rarely recommend surgery due to its risks and the likelihood of cancer recurrence within a year of the procedure.

Celebrating Success Stories at Our Animal Hospital

Our veterinarian specialists in Annapolis are passionate about the work they do to extend and save lives, and we’re extremely proud of the successes that have come and gone through our front doors. Today, we would like to focus on a few memorable patients that we’ve had the privilege of getting to know during their cancer treatment.

Pet Success Stories in Annapolis: Rocco

Rocco was treated at CVSS and Atlantic Veterinary Internal Medicine & Oncology, and just recently graduated from treatment for mast cell tumors.

Pet Success Stories in Annapolis: Delsey

Delsey is a 7-year old Mastiff who had her last treatment for osteosarcoma on March 14.

Pet Success Stories in Annapolis: Thais

Thais is 10 years young and such a sweetie! She recently celebrated the 1-year anniversary for her thyroid carcinoma diagnosis and is cancer-free!

Pet Success Stories in Annapolis: Zena

Zena just graduated from her osteosarcoma treatment (she was too cool to wear her graduation cap).

Mast Cell Tumors

Mast cell tumors (MCT) are quite common in dogs. While they generally appear on the skin, mast cell tumors can also affect other parts of the body, such as the liver, spleen, bone marrow, and GI tract. The tumors can also appear anywhere on the body.

Treatment options for MCT include chemotherapy, surgery, and radiation therapy. It truly depends on the condition of the pet and how far their condition has progressed. Early detection and treatment is the best chance for success.


Bone cancer is a condition most often found in larger breeds, though virtually any breed of dog can be affected. Bone cancer metastasizes quickly and is very aggressive, making an early diagnosis and treatment essential. A common sign of bone cancer in dogs is lameness, which may either develop slowly or suddenly.

Possible treatment options may include amputation or limb-sparing surgery and chemotherapy.

Thyroid Carcinoma

Thyroid carcinoma or thyroid cancer is affects the thyroid glands. Malignant tumors may spread to other organs in the body, and are more common in dogs than cats. A dog with thyroid cancer may not have any obvious clinical symptoms, but they may have a lump or mass on their neck. Masses on the thyroid glands may be surgically removed if possible, or they can be treated with chemotherapy or radiation.