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 bumps 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 bumps that are enlarged, itchy, or ulcerated. Systemic signs such as vomiting or lethargy occur if the tumors release histamines. 

Supportive Care options for a cancer tumor on dog skin involve surgical removal, radiation, chemotherapy, and targeted therapies.

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 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 supportive care options for subcutaneous mast cell tumors. Veterinarians rely on thorough histopathological examinations to support 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 16-20% 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 marks. Mast cell tumors feel firm or soft to the touch. 

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 Signs of Mast Cell Tumors in Dogs?

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

• Appearance: MCTs appear as raised, red bumps 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.

• Itching and Redness: Affected areas become itchy, red, and inflamed. Dogs scratch, lick, or chew at the site, exacerbating the irritation.

• 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.

• Discomfort and Sensitivity: The tumor and surrounding area can be uncomfortable 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?

Signs 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 tumors in dogs less than 12 months of age: a multi-institutional retrospective study,” 2020.

Signs 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 spotted 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.

• 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 are listed below. 

• Edema: The release of histamines and other chemicals from mast cells causes localized enlargement 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 cancer.

• Distant Metastasis: Advanced MCTs spread to distant organs, including the liver, spleen, bone marrow, and lungs.

• 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.

• Limited  Mobility: Tumors located on the limbs or in areas that interfere with movement limiting a dog’s mobility and activity levels, impacting their overall well-being.

How do Veterinarians Spot  Mast Cell Tumors in Dogs?

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

Veterinarians assess the physical signs and medical history of the dog during the clinical examination, looking for signs like skin bumps 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 Help for Mast Cell Tumors in Dogs?

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

Specialized oncology centers provide supportive care for mast cell tumors, as they are experts in handling complex cases. The centers have advanced imaging technologies, such as ultrasound and MRI.

Veterinary oncologists are specialists in cancer support who provides in-depth consultations and develop tailored plans. 

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 support. “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 Options for Mast Cell Tumors in Dogs?

The 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. 

• 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 support signs associated with MCTs and maintain the dog's quality of life. Plans include discomfort management, anti-inflammatory drugs, and antihistamines.

• Monitoring and Follow-up: Regular monitoring and follow-up are necessary to assess plan 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 plan response.

Can Mast Cell Tumors Be Surgically Removed?

Yes, mast cell tumors can be surgically removed. Surgical removal is the first line 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, discomfort management, surgical care, and monitoring for complications are essential.