Mast Cell Tumors In Dogs

Mast cell tumors (MCTs) are one of the most common skin cancers diagnosed in dogs, responsible for approximately 20% of all canine skin tumors¹. These tumors originate from mast cells, a type of white blood cell involved in the body’s allergic responses. MCTs can range from low-grade tumors that are slow-growing and localized to high-grade forms that are more aggressive and more likely to spread or metastasize. Early detection and treatment are crucial for improving patient outcomes.

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Does My Dog Have a Mast Cell Tumor?

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

What are the Signs & Symptoms of Mast Cell Tumors in Dogs?

Mast cell tumors can present in various ways, which sometimes makes these tumors tricky to detect and properly diagnose. Keep an eye out for the following commonly observed signs:

• Visible Skin Mass: A lump or bump on or just under the skin that may appear or change in size over time. It may be soft or firm.
• Redness, Swelling, or Ulceration: Some tumors become inflamed or ulcerated and may resemble a wound or irritated insect bite.
• Itching or Discomfort in a Specific Area: The affected area may cause your dog to lick, scratch, or bite due to histamine that is released by the tumor.
• Digestive Issues: At times, tumors can release histamine systemically, causing vomiting, diarrhea, or decreased appetite.
• Enlarged Lymph Nodes: Lymph node swelling near the site of the tumor can suggest metastasis.

A veterinarian should examine new or changing masses, as MCTs can mimic many other skin conditions.

• 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

How are Mast Cell Tumors in Dogs Diagnosed & Staged?

A fine-needle aspiration (FNA) is commonly the first step in diagnosing a mast cell tumor. An FNA involves using a needle to extract a small sample of cells for analysis under a microscope. If a diagnosis is confirmed, additional tests such as CBC bloodwork (complete blood count), imaging (e.g., X-rays, ultrasound), and a biopsy may be required and used to stage the disease and determine if the cancer has spread to other parts of the body. Refer to this list of diagnostics that are commonly used to diagnose and stage mast cell tumors in dogs. 

• 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

What are the Treatment Options for Canine Mast Cell Tumors?

Treatment for MCTs depends on several factors, including the tumor’s grade, location, and whether metastasis has occurred. The common treatment options for mast cell tumors in dogs include:

• Surgery: For localized tumors, surgical removal with wide margins is often the first and most effective option³. Clean surgical margins reduce the risk of recurrence.
• Radiation Therapy: Stereotactic radiation therapy (SRS/SRT), offered at PetCure Oncology, delivers highly targeted treatment in just a few sessions (usually just 1-3 sessions), minimizing side effects of radiation. Stereotactic radiation is highly targeted and spares healthy tissues. Additionally, if tumors are located in areas of the body that are difficult to operate on completely (think brain, spinal cord, etc.), or if surgical margins are incomplete, radiation therapy can help control local disease. 

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 to CFRT. 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 anesthesia⁶  whereas SRS/SRT requires far fewer sessions, usually just 1-3. 

• Chemotherapy: Chemotherapy is used to treat MCTs that have already spread or have a high risk for spread. Various treatment protocols are available, incorporating multiple drugs as well as corticosteroids.^4,5
• Targeted Therapies: Tyrosine kinase inhibitors (TKIs) like toceranib phosphate (Palladia®) can slow down the growth of tumor cells and might help in treating some types of MCTs.⁸
• Stelfonta® (tigilanol tiglate): An FDA-approved injectable treatment for certain non-metastatic mast cell tumors in dogs. It destroys the tumor cells without surgery.⁹
• Palliative Therapy: Palliative therapies such as antihistamines and painkillers can help maintain quality of life but do not slow progression of the MCT.

Stereotactic Radiation (SRS/SRT) and Canine Mast Cell Tumors

At PetCure Oncology, our centers offer CFRT as well as the newer and more advanced forms of radiation therapy like SRS/SRT. Unlike traditional (CFRT) 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

What is the Life Expectancy, Survival & Prognosis For Dogs with Mast Cell Tumors?

The prognosis for dogs diagnosed with mast cell tumors can vary widely based on the tumor’s grade and whether it has spread. Low-grade tumors that are caught early and completely removed can often be cured. High-grade tumors, as well as those that metastasize, tend to have a more guarded outlook; however, newer treatment options are helping to improve patient outcomes.

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, early diagnosis and treatment improve favorable outcomes. 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.

Frequently Asked Questions About Mast Cell Tumors in Dogs

How long can a dog live with a mast cell tumor?

Prognosis depends on the tumor’s grade and treatment pursued. Dogs with low-grade tumors that are completely resected can live normal lifespans. High-grade tumors may require ongoing treatment and can reduce life expectancy.

Are mast cell tumors in dogs painful?

Some mast cell tumors can cause local irritation or pain, especially if they ulcerate or release histamine. Others may be painless. Watch for signs of pain in your dog, including itching/discomfort, swelling, redness, and/or ulceration.

What causes mast cell tumors in dogs?

While the exact cause is unknown, certain breeds like Boxers, Pugs, and Boston Terriers appear genetically predisposed.¹⁰

Can mast cell tumors in dogs be cured?

Yes, many low-grade tumors are curable with early detection and complete surgical removal or treatment with stereotactic radiation (SRS/SRT). Higher-grade or metastatic cases can often be managed successfully with multimodal therapy.

What breeds are more predisposed to mast cell tumors?

Certain dog breeds appear to be more prone to mast cell tumors, with Boxers and Boston Terriers accounting for nearly half of all cases. Other commonly affected breeds include Pugs, Cocker Spaniels, Bullmastiffs, Fox Terriers, Staffordshire Terriers, Beagles, Bull Terriers, Schnauzers, Weimaraners, and both Labrador and Golden Retrievers.¹⁰

Can radiation be used to treat mast cell tumors in dogs?

Yes. Veterinarians may recommend radiation therapy for mast cell tumors that surgery cannot fully remove or for those located in challenging areas. Stereotactic radiation (SRS/SRT) is a more advanced form of radiation therapy that delivers high doses of radiation with submillimeter precision in as few as 1-3 sessions.

What is the best treatment for mast cell tumors in dogs?

The best approach for MCT treatment depends on the tumor’s grade, location, and whether it has metastasized. Surgery is typically the first step to treating a mast cell tumor, while radiation or chemotherapy may follow in more complex cases, such as those where clean margins are not achievable or when the tumor is in a more sensitive or hard-to-reach area of the body.

How effective is radiation therapy for mast cell tumors in dogs?

Radiation therapy is highly effective for local tumor control, especially when surgery isn’t an option or when clean margins can’t be achieved. Stereotactic radiation (SRS/SRT) can offer highly targeted results in fewer sessions and with minimal damage to surrounding healthy tissues when compared to conventional radiation.

What are the benefits of stereotactic radiation for mast cell tumors?

SRS/SRT delivers high-dose radiation with sub-millimeter accuracy, helping minimize damage and preserve nearby healthy tissue. Fewer sessions (1–3 sessions total) mean fewer anesthetic events, quicker recovery, and minimal side effects, making SRS/SRT an appealing option for many canine mast cell tumor cases.

Is stereotactic radiation better than traditional radiation for dogs with cancer?

While each case is treated individually and results can vary depending on the dog and the tumor, stereotactic radiation can provide similar or better results than traditional radiation therapy. SRS/SRT requires far fewer treatment sessions, which translates into a reduced need for anesthesia along with other benefits like fewer side effects and the potential for faster healing.

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.

• Bindi the Rescue Dog
• Beau & His Journey to Remission
• Information Sheet: Mast Cell Tumors
• Case Study: Canine Mast Cell Tumor

RELATED: Mast Cell Tumors In Cats

REFERENCES
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.
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC10285312/
9. https://pubmed.ncbi.nlm.nih.gov/39417411/
10. https://www.acvs.org/small-animal/mast-cell-tumors/