Mast Cell Tumors in Dogs

Mast Cell Tumors in Canines: Symptoms, Treatment, and Prognosis

Mast cell tumors (MCTs) in dogs are skin cancer tumors originating from mast cells, a type of white blood cell involved in the immune response. 

Mast cell tumors dog signs include red, raised lumps on the skin or subcutaneous masses that vary in severity from benign to malignant. 

The causes of a cancerous red lump on dogs are believed to be genetic predisposition and environmental factors. 

Symptoms of subcutaneous mast cell tumor dog conditions include visible lumps that are swollen, itchy, or ulcerated. Systemic signs such as vomiting or lethargy occur if the tumors release histamines. 

Treatment of a cancer tumor on dog skin involves surgical removal, radiation, chemotherapy, and targeted therapies to manage and control the disease.

What are Mast Cell Tumors in Dogs?

Mast cell tumors in dogs are skin cancers arising from mast cells, which are white blood cells involved in the immune system's response. The responses include allergic reactions and inflammatory processes. The tumors appear anywhere on the body as lumps or bumps on the skin. 

Pet owners who ask, “What is a mast cell tumor?” must know that mast cell tumors in dogs are cancerous red lumps that vary in severity from benign to malignant, spreading to other body parts.

What are Other Terms for Mast Cell Tumors in Dogs?

The other terms for mast cell tumors in dogs are mastocytomas or round cell tumors. "Mastocytoma" refers to a benign form of mast cell tumor, while "round cell tumor" is a broader category that includes MCTs and similar tumors. 

Differentiating between the terms is crucial for determining the treatment and prognosis of subcutaneous mast cell tumors. Veterinarians rely on thorough histopathological examinations to diagnose and differentiate the tumor types.

How do Mast Cell Tumors Develop in Dogs?

Mast cell tumors develop in dogs through genetic predispositions, mutations in regulatory genes, cellular proliferation, and interactions with environmental and immunological factors. “Canine mast cell tumors may develop through novel mutations in the proto-oncogene c-kit, involving exons 11 and 12,” according to the study by London, C., London, C., Galli, S., Yuuki, T., Hu, Z., Helfand, S., & Geissler, E. titled “Spontaneous canine mast cell tumors express tandem duplications in the proto-oncogene c-kit,” 1999.

Genetic mutations play a role in the development of mast cell tumors, altering the growth and function of mast cells. Exposure to environmental triggers such as toxins, radiation, or inflammation stimulates the abnormal growth of mast cells, leading to tumor formation.

How Common are Mast Cell Tumors in Dogs?

Mast cell tumors in dogs are very common. The tumors account for 16-2o% of all skin tumors in canines. “The most common skin tumor in dogs is the mast cell tumor (MCT), with an incidence of close to 20% in the canine population,” according to the study by London, C., & Séguin, B. titled “Mast cell tumors in the dog,” 2003.

MCTs are prevalent in certain breeds, such as Boxers, Bulldogs, Boston Terriers, and Labrador Retrievers. Mast cell tumors are common in dogs but are less frequent in cats and puppies.

What are the Common Locations Where Mast Cell Tumors Occur in Dogs?

The common locations where mast cell tumors occur in dogs are on the trunk, limbs, perineal area, and internal organs.

The presentation of mast cell tumors in dogs reflects that the tumors originate from mast cells in the connective tissues of the skin and mucosal membranes. 

Skin tumors are the most common, and internal organ involvement poses more severe risks. Mast cell tumors appear in less common locations, such as the ears, eyes, nose, and genitalia.

Which Breeds Are More Prone to Developing Mast Cell Tumors?

The breeds more prone to developing mast cell tumors are listed below.

  • Boxers: Boxers are one of the most commonly affected breeds, often developing multiple MCTs throughout their lifetime.
  • Bulldogs: English and French Bulldogs are at increased risk for mast cell tumors.
  • Golden Retrievers: Golden Retrievers are prone to various types of cancer, including MCTs.
  • Pugs: Pugs frequently develop MCTs, which are located on their skin.
  • Labrador Retrievers: Labrador Retrievers have a higher incidence of MCTs than the general dog population.
  • Shar-Peis: Shar-Peis develop more aggressive forms of MCTs at a younger age.
  • Boston Terriers: Boston Terriers show a higher predisposition to developing mast cell tumors.
  • Staffordshire Bull Terriers: Staffies have a notable risk for MCTs, presenting with tumors at younger ages.

What do Mast Cell Tumors in Dogs Look Like?

Mast cell tumors in dogs look like lumps or masses on the skin, varying in size, color, and texture. Pictures of mast cell tumors in dogs show raised, red, and ulcerated lesions. Mast cell tumors feel firm or soft to the touch. The mast cell tumor dog picture below illustrates the condition.

What are the Causes of Mast Cell Tumors in Dogs?

The causes of mast cell tumors in dogs are listed below.

  • Genetic Predisposition: Genetic factors, such as mutations in the c-KIT gene, contribute to the development of mast cell tumors.
  • Environmental Factors: Exposure to pesticides, herbicides, and industrial chemicals increases the risk of developing MCTs by inducing genetic mutations and promoting tumor growth.
  • Immune System Dysregulation: Abnormalities in mast cell regulation leads to uncontrolled growth and tumor formation. Dysregulated immune responses, such as autoimmune diseases or chronic allergic conditions, contribute to mast cell proliferation and tumorigenesis.
  • Hormonal Influences: Hormonal imbalances and fluctuations affect mast cell activity and proliferation, promoting tumor development. 

Are Dogs with Autoimmune Diseases More Likely to Get Mast Cell Tumors?

Yes, dogs with autoimmune diseases are more likely to get mast cell tumors due to the underlying dysregulation of their immune system. Research shows that the chronic inflammation and immune system dysfunction of autoimmune diseases enable MCT growth. “About 10-20% of mast cell tumors in dogs express mutant KIT receptors, suggesting a connection between autoimmune diseases and mast cell tumors,” according to the study by Amagai, Y., & Tanaka, A. titled “Mast Cell Tumors,” 2016.

The abnormal immune response caused by an autoimmune disease leads to an overstimulation of mast cells, triggering their uncontrolled growth and proliferation. 

What are the Symptoms of Mast Cell Tumors in Dogs?

The symptoms of mast cell tumors in dogs are listed below.

  • Appearance: MCTs appear as raised, red lumps on the skin or as subcutaneous masses beneath the skin.
  • Fluctuation: The lumps change in size over time, rapidly enlarging or shrinking due to the release of histamines and other chemicals from the mast cells.
  • Ulceration: The tumors ulcerate, leading to open sores or wounds on the skin.
  • Itching and Redness: Affected areas become itchy, red, and inflamed. Dogs scratch, lick, or chew at the site, exacerbating the irritation and causing secondary infections.
  • Gastrointestinal Issues: MCTs release histamines and other substances into the bloodstream, leading to symptoms like vomiting, diarrhea, and loss of appetite.
  • Lethargy: Dogs with MCTs exhibit general lethargy or decreased activity levels due to discomfort or the tumor's systemic effects.
  • Swelling: Swelling around the tumor site is expected due to inflammation or the accumulation of fluids.
  • Pain and Sensitivity: The tumor and surrounding area are painful or sensitive to touch.
  • Lymph Node Enlargement: Nearby lymph nodes are enlarged if the cancer has spread.
  • Other Organ Involvement: MCTs metastasize to internal organs such as the liver, spleen, or bone marrow, leading to severe systemic symptoms.

When do Symptoms of Mast Cell Tumors Usually Occur in Dogs?

Symptoms of mast cell tumors usually occur in dogs under one year. “Mast cell tumors in dogs less than 12 months old usually occur at a median age of 7.6 months at first presentation and 9 months at diagnosis,” according to the study by Rigas, K., Biasoli, D., Polton, G., Finotello, R., Murphy, S., Palma, S., Starkey, M., & Verganti, S. titled “Mast cell tumours in dogs less than 12 months of age: a multi-institutional retrospective study,” 2020.

Symptoms appear several weeks to months after the tumor develops. Factors such as the grade of the tumor (low, intermediate, or high), as well as its size and location, determine how quickly clinical signs manifest.

What are the Risk Factors for Mast Cell Tumors in Dogs?

The risk factors for mast cell tumors in dogs are listed below. 

  • Breed Predisposition: Certain breeds have a higher genetic predisposition to developing MCTs due to inherited genetic factors.
  • Age: MCTs are commonly diagnosed in older dogs between the ages of 8 and 10 but occur at any age.
  • Specific Gene Mutations: Mutations in certain genes, such as c-KIT, are associated with the development of MCTs. The mutations lead to uncontrolled mast cell proliferation.
  • Chronic Inflammatory Conditions: Dogs with chronic inflammatory conditions or frequent allergic reactions are at a higher risk of developing MCTs. Chronic inflammation stimulates mast cell proliferation and tumor formation.
  • Exposure to Carcinogens: Environmental toxins and carcinogens, such as pesticides, herbicides, and industrial chemicals, increase the risk of developing MCTs. Long-term exposure to the substances leads to genetic mutations and cancer.
  • Hormonal Imbalances: Hormones like estrogen impact mast cell behavior and proliferation, but the exact mechanisms are not fully understood.
  • Immune System Abnormalities: An improperly functioning immune system fails to regulate mast cell activity, leading to tumor growth.
  • Previous Tumors: Dogs that previously had mast cell tumors are at a higher risk of additional tumors due to genetic predispositions or remaining abnormal mast cells.

What are the Complications of Mast Cell Tumors in Dogs?

The complications of mast cell tumors in dogs that can arise during or after treatment are listed below. 

  • Ulceration and Infection: MCTs ulcerate and lead to open sores susceptible to secondary bacterial infections. 
  • Swelling and Edema: The release of histamines and other chemicals from mast cells causes localized swelling and fluid accumulation (edema) around the tumor site, leading to pain and discomfort.
  • Anaphylactic Reactions: The release of histamine and other inflammatory mediators from the tumor causes severe allergic reactions, including anaphylaxis. 
  • Gastrointestinal Issues: Histamine release stimulates gastric acid secretion, causing gastrointestinal problems such as ulcers, vomiting, diarrhea, and appetite loss. 
  • Spread to Lymph Nodes: MCTs metastasize to regional lymph nodes, enlarging them and spreading the disease.
  • Distant Metastasis: Advanced MCTs spread to distant organs, including the liver, spleen, bone marrow, and lungs, complicating treatment.
  • Blood Clotting Disorders: The release of chemicals by mast cells affects blood clotting, leading to disorders such as disseminated intravascular coagulation (DIC), which causes abnormal bleeding or clotting issues.
  • Recurrence: There is a risk of recurrence at the original site or the development of new MCTs elsewhere in the body. Dogs with one MCT are at increased risk of developing additional tumors.
  • Chronic Pain and Discomfort: The presence of MCTs, if they are ulcerated or infected, causes chronic pain and discomfort.
  • Reduced Mobility: Tumors located on the limbs or in areas that interfere with movement reduce a dog’s mobility and activity levels, impacting their overall well-being.

How do Veterinarians Diagnose Mast Cell Tumors in Dogs?

Veterinarians diagnose mast cell tumors in dogs through clinical examination, biopsy, and histological analysis. 

Veterinarians assess the physical symptoms and medical history of the dog during the clinical examination, looking for signs like skin lumps or gastrointestinal issues that indicate a mast cell tumor. 

Biopsy, which involves removing a tissue sample from the tumor, is analyzed to confirm the presence of mast cells. 

Histological analysis, which examines the tissue microscopically, helps identify the tumor's specific characteristics, such as cell type and growth patterns. 

Where Can You Seek a Diagnosis for Mast Cell Tumors in Dogs?

You can seek a diagnosis for mast cell tumors in dogs at specialized oncology centers and consultations with veterinary oncologists. 

Specialized oncology centers diagnose and treat mast cell tumors, as they are experts in handling complex cases. The centers have advanced imaging technologies, such as ultrasound and MRI, that aid in diagnosis. 

Veterinary oncologists are specialists in cancer treatment that provide in-depth consultations and develop tailored treatment plans. 

What is the Typical Prognosis for Dogs with Mast Cell Tumors After Treatment?

The typical prognosis for dogs with mast cell tumors after treatment varies depending on the tumor's grade, stage, and location. Some dogs achieve long-term survival, while others have a more guarded outlook. “Aggressive local therapy combined with systemic chemotherapy (prednisone, vinblastine, and CCNU) can provide a median survival in excess of 40 months for dogs with grade II stage 2 mast cell tumors,” according to the study by Lejeune, A., Skorupski, K., Skorupski, K., Frazier, S., Frazier, S., Frazier, S., Vanhaezebrouck, I., Vanhaezebrouck, I., Rebhun, R., Rebhun, R., Reilly, C., Reilly, C., Rodriguez, C., & Rodriguez, C. titled “Aggressive local therapy combined with systemic chemotherapy provides long-term control in grade II stage 2 canine mast cell tumour: 21 cases (1999-2012).” 2015. 

Factors that influence the prognosis of mast cell tumors in dogs include the presence of metastasis, the pet's overall health condition, and how the tumor responds to treatment. 

Can Mast Cell Tumors Be Mistaken for Other Types of Growths or Conditions?

Yes, mast cell tumors can be mistaken for other types of growths or conditions, such as benign skin lumps or other types of skin cancer. “Mast cell tumors are tricky and difficult to deal with because they appear as a large central tumor but are in fact surrounded by a halo of smaller, microscopic nests of mast cells that infiltrate normal-looking skin,” according to the article by Villalobos, A. titled “Tumors of the Skin in Dogs,” 2018.

A differential diagnosis is necessary to distinguish mast cell tumors from other conditions. The process involves physical examinations, imaging tests, and sample biopsies to differentiate between various skin abnormalities. The characteristics of mast cell tumors, such as their tendency to release histamine and other chemicals, aid in the differentiation.

How Long Can a Dog Survive with Mast Cell Tumors?

How long a dog can survive with mast cell tumors varies from a few months to 1-2 years, depending on the tumor's grade, stage, and response to treatment. “The median survival time for dogs with grade III mast cell tumors was 331 days, with 45% of dogs alive at 1 and 2 years,” according to the study by Thamm, D., Mauldin, E., & Vail, D. titled “Prednisone and vinblastine chemotherapy for canine mast cell tumor--41 cases (1992-1997),” 1999.

Factors like tumor aggressiveness, metastasis, overall health, the dog's breed, and age influence survival rates. Regular vet check-ups, treatment adherence, and a supportive environment improve quality of life and extend survival times.

Are Mast Cell Tumors Typically benign or Malignant?

Mast cell tumors in dogs are equally likely to be benign or malignant, with malignant forms being more aggressive and requiring intensive treatment. “Approximately 50% of mast cell tumors in dogs are malignant,” according to the study by O'keefe, D. titled “Canine mast cell tumors,” 1990.

Benign tumors have well-defined borders and a slower growth rate compared to malignant tumors that infiltrate surrounding tissues and metastasize to other organs. Malignant tumors exhibit more pleomorphism and a higher mitotic index, indicating their highly proliferative nature.

What are the Treatment Options for Mast Cell Tumors in Dogs?

The treatment options for mast cell tumors in dogs are listed below.

  • Surgical Removal (Excision): Surgical excision removes the mast cell tumor and a surrounding margin of healthy tissue to ensure complete removal of the cancerous cells. Specialized surgical techniques are employed in challenging areas to ensure complete removal while preserving function and appearance.
  • Radiation Therapy: Radiation therapy uses high-energy beams to target and destroy cancer cells. The treatment is used after surgery to eliminate any remaining cancer cells, treat inoperable tumors, or alleviate symptoms in advanced cases.
  • Chemotherapy: Chemotherapy involves administering drugs that target rapidly dividing cells, including cancer cells. Common chemotherapy drugs for MCTs include vinblastine, lomustine, and prednisone.
  • Targeted Therapies: Targeted therapies like toceranib phosphate (Palladia®) specifically inhibit receptors on mast cells, blocking signals that promote tumor growth. Therapies are used alone or with surgery or chemotherapy, depending on the case.
  • Symptomatic Management: Symptomatic management aims to alleviate symptoms associated with MCTs and improve the dog's quality of life. Treatment includes pain management, anti-inflammatory drugs, and antihistamines.
  • Monitoring and Follow-up: Regular monitoring and follow-up are necessary to assess treatment response. Management includes physical exams, imaging studies, and blood tests to evaluate tumor markers, with frequency and duration varying based on tumor stage, grade, and treatment response.

Can Mast Cell Tumors Be Surgically Removed?

Yes, mast cell tumors can be surgically removed. Surgical removal is the first line of treatment for MCTs if the tumor is localized and accessible. “Most grade I and II cutaneous mast cell tumors in dogs can be successfully treated by complete surgical removal with margins smaller than those currently recommended,” according to the study by Schultheiss, P., Gardiner, D., Rao, S., Olea-Popelka, F., & Tuohy, J. titled “Association of histologic tumor characteristics and size of surgical margins with clinical outcome after surgical removal of cutaneous mast cell tumors in dogs,” 2011.

The surgical goal is to complete tumor removal while preserving healthy tissue. Post-surgery, pain management, wound care, and monitoring for complications are essential. 

Can CBD Oil Effectively Treat Symptoms of Mast Cell Tumors in Dogs?

Yes, CBD oil can effectively treat symptoms of mast cell tumors in dogs, such as pain and inflammation, although its effectiveness varies. “Oral transmucosal cannabidiol (CBD) in combination with anti-inflammatory drugs, gabapentin, and amitriptyline improves owner-reported pain scores and quality of life in dogs,” according to the study by Brioschi, F., Cesare, F., Gioeni, D., Rabbogliatti, V., Ferrari, F., D'urso, E., Amari, M., & Ravasio, G. titled “Oral Transmucosal Cannabidiol Oil Formulation as Part of a Multimodal Analgesic Regimen: Effects on Pain Relief and Quality of Life Improvement in Dogs Affected by Spontaneous Osteoarthritis,” 2020.

Research indicates that CBD oil alleviates discomfort in dogs with mast cell tumors. Consult with a veterinarian before using CBD oil for the dog's condition.