Mast Cell Tumors In Dogs

Mast cell tumors (MCTs) are common in dogs, accounting for approximately 20 percent of all skin tumors in dogs.1  They can be very invasive and often regrow after surgical removal; they may also spread (metastasize). MCTs can arise from any skin site on the body and can have a variety of appearances. Any lump or bump on your dog should be looked at by a veterinarian. Some MCTs release histamine, which can cause swelling and bruising around the tumor. MCTs can be treated successfully if diagnosed early.

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Does My Dog Have a Mast Cell Tumor?

Bindi a mast cell cancer surviving dog 18 month after SRS treatment.

MCTs are usually a skin cancer in dogs, but they can spread to lymph nodes, internal organs and bone marrow. MCTs can occur in any dog regardless of breed or sex. However, some breeds including Boxers, Boston Terriers, Golden Retrievers, and schnauzers are at higher risk.

When we adopted Bindi in December of 2014 she had a small bump on the bridge of her nose. Over time the bump grew in size and we took her to see our local veterinarian. A biopsy confirmed a mast cell tumor. -Mack Hussey, Pet Parent to Pet Hero Bindi

Signs & Symptoms of Mast Cell Tumors in Dogs

If your pet displays these signs or symptoms of a mast cell tumor, have your pet examined by your primary care veterinarian as soon as possible.

  • Mass Lesion Involving the Skin or Subcutaneous Tissue At Any Body Location – Individual tumor appearance is highly variable:
    • Some lesions are ulcerated, others are covered with hair
    • Redness, bruising and fluid buildup (edema) can occur, and may worsen with manipulation or scratching
    • Tumors can fluctuate up and down in size
  • Enlarged Lymph Nodes – Swelling and enlargement of lymph nodes can appear near areas of tumor involvement
  • Gastrointestinal Symptoms – Loss of appetite, vomiting or diarrhea
  • Other Signs of Cancer – While the above are some of the common signs of a mast cell tumor, there are other signs of cancer. For example, weight loss, weight gain, a persistent cough, and wounds that won’t heal are also signs of cancer. Read our “Top 10 Warning Signs of Cancer in Your Pet” post for more information

Diagnosis & Staging

  • Blood and urine samples – These tests will assess organ function and identify concurrent diseases
  • Abdominal ultrasound – This will assess abdominal organs for evidence of MCT spread
  • Fine Needle Aspirates – An aspirate is a small biopsy. This is used to diagnose MCT spread, especially to skin, lymph nodes, and internal organs
  • Chest Radiographs – This imaging will evaluate heart and lungs before anesthesia, and check for concurrent diseases including cancer spread
  • Tissue Biopsy – This biopsy allows microscopic evaluation of the primary MCT, providing confirmation of diagnosis and a tumor grade (low or high)2
  • CT Scan – This imaging identifies the precise location and size of MCTs for detailed surgery or radiation planning

Treatment Options for Mast Cell Tumors

A diagnosis can be scary, but the good news is that treatment options are available for your pet.


Surgery is the ideal treatment for MCTs, as long as the cancer can be completely removed and has not already spread.3


Chemotherapy is used to treat MCTs that have already spread, or have a high risk for spread. A variety of treatment protocols are available incorporating multiple drugs as well as corticosteroids.4,5

Palliative Therapy

Palliative therapies such as antihistamines and pain killers can help maintain quality of life but do not slow progression of the MCT.

Radiation Therapy

Before the introduction of Stereotactic Radiation (SRS/SRT) in veterinary medicine, the most advanced radiation therapy available to pet owners was conventionally fractionated radiation therapy (CFRT). CFRT can be used alone or following a surgery where some cancer cells remain. CFRT can treat the tumor in ways surgery or chemotherapy can’t and in many cases is the recommended course of treatment, but there are also disadvantages. The radiation delivered to the tumor can damage the normal, healthy tissue surrounding it. A typical treatment course for MCT usually involves approximately 15 separate treatment sessions under anesthesia.6

Stereotactic Radiation (SRS/SRT)

At PetCure Oncology, our centers offer CFRT as well as the newer and more advanced forms of radiation therapy like SRS/SRT. Unlike traditional radiation therapy, SRS/SRT is able to deliver high doses of radiation with sub-millimeter precision. This means:

  • Maximum damage to the tumor and minimal collateral damage to healthy tissues nearby
  • Fewer treatment sessions compared to CFRT—patients require only 1-3 sessions, which means fewer anesthetic events, more safety, and less disruption to your schedule
  • Fast recovery with little to no side effects
  • Ability to treat tumors previously considered untreatable
  • PetCure Oncology’s radiation oncologists are experienced using SRS/SRT to treat dogs with MCTs

Dog Mast Cell Tumors: Life Expectancy, Survival & Prognosis

Prognosis varies by case, but oftentimes:

  • Localized low grade MCTs can often be cured if:
    • They are completely removed with surgery3
    • They are incompletely removed with surgery but also receive conventional radiation therapy6
  • MCTs that have spread to local lymph nodes can still have a good prognosis after treatment including surgery, radiation, and chemotherapy
    • Survival times over 5 years are reported7
  • High grade MCTs or MCTs that have spread to several sites have a guarded prognosis2
    • Treatment may include chemotherapy, radiation therapy, and surgery
    • Expected survival may only be a few months, even with treatment

As with any cancer, the earlier it is diagnosed and treated, the better the chances that treatment will be successful. If you have an appointment to discuss radiation therapy for your pet’s mast cell tumor, here are some questions to ask your veterinary oncologist.

Meet Our Mast Cell Tumor Pet Hero

Meet our inspiring Pet Hero that has fought a mast cell tumor. We invite you to read her story. If your pet has been diagnosed with cancer, contact our Pet Advocates at 833-738-4376 or your local PetCure Oncology center. Our team members are ready to help answer your questions.

RELATED: Mast Cell Tumors In Cats

1. https://vth.vetmed.wsu.edu/specialties/oncology/information-for-owners/mast-cell-cancer
2. Kiupel M, Webster JD, Bailey KD et al. Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biological behavior. Vet Pathol 2011;48:147-155.
3. Seguin B, Leibman N, Bregazzi VS et al. Clinical outcome of dogs with grade-II mast cell tumors treated with surgery alone: 55 cases (1996-1999). J Am Vet Med Assoc 2001;218:1120-1123.
4. Rassnick KM, Moore AS, Williams LE et al. Treatment of canine mast cell tumors with CCNU (lomustine). J Vet Intern Med 1999;13:601-605.
5. London CA, Malpas PB, Wood-Follis SL et al. Multi-center, placebo-controlled, double-blinded, randomized study of oral toceranib phosphate (SU11654), a receptor tyrosine kinase inhibitor, for the treatment of dogs with recurrent (either local or distant) mast cell tumor following surgical excision. Clin Cancer Res 2009;15:3856-3865.
6. Al Sarraf R, Mauldin GN, Patnaik AK et al. A prospective study of radiation therapy for the treatment of grade 2 mast cell tumors in 32 dogs. J Vet Intern Med 1996;10:376-378.
7. Lejeune A, Skorupski K, Frazier S et al. Aggressive local therapy combined with systemic chemotherapy provides long-term control in grade II stage 2 canine mast cell tumour: 21 cases (1999-2012). Vet Comp Oncol 2015;13:267-280.
Types of Cancers in Dogs

If your dog is displaying any symptoms of cancer or has been diagnosed with cancer, sort below by cancer type or tumor location to learn more about the most common types of cancer in dogs and available treatment options. Click on the links for more specific information on treatment and real patient stories.


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