Roxy Cruise loves daily walks around the neighborhood, guard duty to protect her home from squirrels, birds and even butterflies, gnawing constantly on antler snacks, cuddling with her owner so closely she’s virtually a shadow, and explaining her day to passers-by whenever she decides it’s bark-o’clock. And, if she knew the details, she’d love the staff at CARE, who have enabled this irresistible pit bull to survive six years so far after being diagnosed with mast cell cancer.

Roxy Cruise

Roxy Cruise

What Is a Mast Cell Tumor?

Mast cells live in connective tissue and contain granules that carry histamine and heparin. The release of histamine causes itching, swelling, redness, edema and all the things dogs (or people) experience during an allergic reaction. When too much histamine is released into the body, it can cause anaphylaxis, a life-threatening, systemic allergic reaction.

These white blood cells can start to divide rapidly and form a tumor. Mast cell tumors (MCTs) are a common malignant skin cancer in dogs, though they’re almost always benign in cats. Boxers, Boston terriers and pugs seem to be more susceptible than other breeds.

Owners know to look for lumps on their pet during grooming or petting, and a veterinarian will determine whether they’re malignant or benign. Dogs can have one MCT or several. They may resemble an insect bite and induce itching, they’re frequently raised and reddened, and they may change in size but do not go away.

Roxy’s Long Journey to Health

In August 2017, Roxy came to CARE as a 7-year-old spayed pit bull whose owner had adopted her 14 months earlier. Roxy had already had surgery on her right forelimb and left leg to remove two masses, which were sent for histopathology and showed MCTs. After that, more masses popped up on her belly, the right side of the chest, abdomen, knee and thigh. The doctor removed them all and started chemotherapy, prescribing CCNU (an agent that disrupts DNA transcription and RNA replication) followed by Chlorambucil.

At the end of 2018, Roxy developed more tumors. This time, vets started her on Vinblastine chemotherapy. The cancer remained stable for a long time, and she went back into surgery in early 2020 to remove the visible tumors. At this point, the disease had become more aggressive and spread to lymph nodes in her groin.

After that surgery, Roxy received Torigen immunotherapy vaccinations and began oral Palladia chemotherapy. Her cancer responded well until mid-2021, when she developed new MCTs and had another surgery to remove them. She’s remained on supportive care medications and pulse-doses of prednisone (a steroid used to treat MCT) ever since and is now 13.

Complications With Mast Cell Tumors

Though tumors from mast cell cancer most commonly appear as nodules on the skin, they can also form inside the body, affecting intestines, liver and spleen. MCTs found in the mouth, on the muzzle, or around the genitals tend to behave more aggressively than those in other parts of the body.

Some MCTs spread to other locations, such as lymph nodes or internal organs. Even if they don’t, they can cause disease through the release of histamine, which increases stomach acid production and can result in stomach ulcers.

How Vets Diagnose MCTs

After examining your pet’s lump, your vet will perform a fine needle aspiration, collecting a cell sample and viewing it under a microscope in search of mast cells. If the diagnosis is positive, the pet will probably need surgery to remove the mass and prevent it from spreading to other areas. Higher-grade tumors are more likely to regrow or metastasize around the body.

Treatment options depend on the grade and stage of the tumor. For example, low-grade tumors are frequently handled by complete surgical removal. For smaller tumors, vets will generally remove 1 to 3 centimeters of healthy tissue from all sides of the tumor, to ensure removal of tiny clusters of mast cells circling the mass.

High-grade tumors can regrow or spread within months of diagnosis, and surgery alone rarely provides more than three to six months of extra life. Vets recommend oral or intravenous chemotherapy to slow or stop the progression of the disease, sometimes augmenting it with radiation therapy. Dogs treated that way can live for years beyond their diagnosis if careful owners monitor their health – as Roxy may well do.

Charlotte Animal Referral and Emergency is the pet version of a human medical center. CARE offers all types of treatments, from emergency attention 24 hours a day and 365 days a year to board-certified specialty care after a referral from your primary veterinarian. Please take a visual tour of the practice at

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