Mast cells are a type of white blood cell found throughout a cat’s body, including the skin, respiratory system, and digestive tract. These cells are crucial components of the immune system, storing histamine – a chemical compound released in response to allergens. Histamine’s role is to trigger the body’s defenses against perceived threats.
When a mast cell encounters an allergen, it undergoes degranulation, releasing histamine. This release causes common allergy symptoms like sneezing, itching, and runny nose or eyes, as the body attempts to expel the allergen. However, when histamine is released in excessive amounts, it can lead to a severe, life-threatening allergic reaction known as anaphylaxis.
A mast cell tumor (MCT) develops when mast cells replicate and divide uncontrollably in tissues. These tumors can be slow-growing over months or years, or they can appear and grow rapidly, sometimes seemingly overnight.
In cats, mast cell tumors are most frequently found on the skin (cutaneous MCTs), particularly on the head and neck, although they can occur anywhere on the body. Cutaneous MCTs are the second most common type of skin tumor in cats. Mast cell tumors can also affect internal organs, such as the spleen (visceral or splenic MCTs) and the intestinal tract (intestinal MCTs), most often in the small intestines.
Are Mast Cell Tumors Cancerous in Cats?
Tumors are classified as either benign or malignant, which significantly impacts their behavior and prognosis:
- Benign Tumors: These are non-cancerous growths that do not invade surrounding tissues or spread to other parts of the body (metastasize). Benign mast cell tumors typically grow slowly and generally have a favorable prognosis.
- Malignant Tumors: These are cancerous tumors composed of abnormal cells that divide rapidly. Malignant tumors aggressively invade nearby tissues and can spread to distant sites through the bloodstream or lymphatic system. Malignant MCTs are generally more aggressive and carry a less favorable long-term prognosis.
In cats, mast cell tumors can be either benign or malignant, depending on the specific characteristics of the mast cells within the tumor and its location. Cutaneous mast cell tumors in cats are often benign, whereas mast cell tumors affecting internal organs are more likely to be malignant and pose a greater health risk.
Recognizing the Signs: Symptoms of Mast Cell Tumors in Cats
The clinical signs of mast cell tumors in cats can vary widely, depending on the tumor’s location (cutaneous, splenic, or intestinal) and whether it is benign or malignant. Tumors located on the spleen or within the intestinal tract are more likely to cause systemic or whole-body symptoms due to the widespread release of histamine and other substances from the tumor cells.
Cutaneous Mast Cell Tumor Symptoms:
- Skin Plaques: Hard, raised, hairless, and flattened bumps or plaques on the skin. These are commonly found on the head and neck but can appear anywhere on the cat’s body.
- Nodules: Small, firm lumps or nodules within the skin that feel solid upon touch.
- Itchiness (Pruritus): Excessive scratching, licking, or biting at the tumor site, often leading to hair loss, skin irritation, and secondary infections.
- Ulceration: Open sores or ulcers may develop on the surface of the tumor, which can bleed or ooze.
Splenic or Visceral Mast Cell Tumor Symptoms:
- Vomiting: Frequent or persistent vomiting, which may or may not be related to meals.
- Weight Loss: Unexplained and progressive weight loss despite a normal or increased appetite in some cases.
- Poor Appetite (Anorexia): Decreased interest in food or complete refusal to eat.
Intestinal Mast Cell Tumor Symptoms:
- Vomiting and Diarrhea: Gastrointestinal upset, including both vomiting and diarrhea, which can be chronic or intermittent.
- Blood in Stool (Hematochezia): Fresh, red blood visible in the feces, indicating bleeding in the lower digestive tract.
- Dark, Tarry Stool (Melena): Black or tarry stools, which suggest digested blood from bleeding in the upper digestive tract.
What Causes Mast Cell Tumors in Cats?
The precise cause of mast cell tumors in cats is not completely understood. However, it is believed that a combination of genetic predisposition and environmental factors contribute to their development.
- Genetics: Certain breeds, like Siamese cats, appear to have a higher predisposition to developing cutaneous mast cell tumors, suggesting a genetic component.
- KIT Gene Mutation: In dogs, mutations in the KIT gene are strongly linked to mast cell tumor development. The KIT protein is involved in cell growth and division. Similar KIT gene mutations have also been identified in cats with mast cell tumors, indicating a possible role in feline MCTs as well.
- Environmental Factors: While less defined, environmental factors could potentially play a role in mast cell tumor development in cats, although more research is needed in this area.
Diagnosis: How Veterinarians Detect Mast Cell Tumors in Cats
Diagnosing mast cell tumors in cats typically involves a combination of physical examination, cytology, and potentially histopathology.
- Fine Needle Aspiration (FNA): This is often the first diagnostic step. A veterinarian inserts a thin, sterile needle into the tumor to collect a small sample of cells. The cells are then placed on a slide and examined under a microscope (cytology). Mast cells have a distinctive appearance, and abnormalities associated with tumors are usually readily identifiable through cytology. FNA is a minimally invasive and rapid method for initial diagnosis.
- Biopsy and Histopathology: In some cases, or to confirm FNA findings and obtain more detailed information, a biopsy may be recommended. This involves surgically removing a small piece of the tumor tissue or the entire tumor. The tissue sample is then submitted to a veterinary pathologist for histopathology. Histopathology provides a more comprehensive evaluation of the tumor cells, including tumor type, grade (aggressiveness), and whether surgical margins are clean (meaning no tumor cells are detected at the edges of the removed tissue). Clean surgical margins are crucial for preventing tumor recurrence after surgical removal.
- Additional Diagnostics: If systemic symptoms are present, or if a malignant mast cell tumor is suspected or confirmed, further diagnostic tests may be necessary. These can include bloodwork (complete blood count and serum biochemistry), urinalysis, and imaging studies such as chest and abdominal X-rays or ultrasound. These tests help to assess the cat’s overall health, stage the disease (determine if and where the cancer has spread), and guide treatment planning and prognosis.
Treatment Options for Feline Mast Cell Tumors
Treatment for mast cell tumors in cats is tailored to the tumor’s location, type (benign or malignant), and extent of spread.
- Surgical Removal: Surgery is the primary and often most effective treatment for cutaneous mast cell tumors in cats. Complete surgical excision with clean margins is the goal. For splenic and intestinal mast cell tumors, complete surgical removal may not always be possible, especially if the tumor has spread.
- Chemotherapy: Chemotherapy may be recommended for malignant mast cell tumors, particularly those that are splenic, intestinal, or have metastasized. Chemotherapy drugs can help to slow tumor growth, reduce tumor size, and manage systemic disease.
- Radiation Therapy: Radiation therapy is another treatment option, particularly for tumors that cannot be completely removed surgically or for localized control of aggressive tumors.
- Medications to Manage Symptoms: Regardless of the primary treatment, medications are often prescribed to manage symptoms associated with mast cell tumors. These commonly include:
- Antihistamines: To block the effects of histamine released by tumor cells, reducing allergy-like symptoms and systemic effects.
- Antacids: To protect the gastrointestinal tract from excess stomach acid production, which can be stimulated by histamine.
- Anti-nausea Medications (Antiemetics): To control nausea and vomiting, especially in cases of splenic or intestinal tumors.
- Pain Medications (Analgesics): To manage pain and discomfort associated with tumors or surgery.
Recovery and Prognosis for Cats with Mast Cell Tumors
The prognosis for cats with mast cell tumors varies considerably depending on the tumor type and location.
- Cutaneous Mast Cell Tumors: Most cats with benign cutaneous mast cell tumors that are surgically removed with clean margins have an excellent prognosis and can live normal, healthy lives. Recurrence is uncommon if removal is complete.
- Splenic or Intestinal Mast Cell Tumors: Cats with splenic or intestinal mast cell tumors typically have a less favorable prognosis, as these tumors are often malignant and have a higher risk of metastasis. Prognosis depends on the extent of the disease and response to treatment (chemotherapy, etc.). Long-term management often involves medications to control systemic symptoms and improve quality of life.
Post-operative care after surgical removal of a mast cell tumor is crucial. An Elizabethan collar (E-collar or recovery cone) is usually necessary to prevent the cat from licking or scratching at the surgical site, which can cause self-trauma and delay healing. Keeping the surgical site clean and dry is essential, and limiting the cat’s activity for 10-14 days helps to prevent wound dehiscence (opening). Regular follow-up veterinary visits are important to monitor for recurrence or complications. If any concerns arise during the recovery period at home, prompt contact with the veterinary clinic is recommended.
