Claim of the Month: Mast Cell Tumor

Black and white French bulldog with an orange collar outside in nature

Claim of the Month: Mast Cell Tumor

Pet: Daisy*, a 5-year-old spayed female French Bulldog


Daisy’s Story

Pampered Frenchie, Daisy, had suffered from allergies and dermatological issues for most of her life, so her family paid close attention to her skin. This spring, they noticed something different. A red, raised lump appeared on the skin over Daisy’s right elbow. Some days, it appeared redder and more prominent, while other days, it was barely noticeable. When it didn’t disappear after a week or two, they scheduled an appointment with their family veterinarian.

When the vet examined the lump, she explained that a visual inspection couldn’t give them all of the answers they needed. Some dogs with allergies could develop benign cysts or infections of the hair follicle that looked just like Daisy’s lump. On the other hand, some serious tumors could present with the exact same appearance. This meant that just “keeping an eye” on the mass could have dangerous consequences. Being proactive, Daisy’s family agreed to let their vet perform some preliminary tests. The vet used a small needle to collect some cells from the lump and examined the sample under a microscope. Numerous round cells with dark-staining granules filled the slide:  a hallmark sign of a malignant cutaneous mast cell tumor.

About the Condition: Mast Cell Tumors

Mast cell tumors represent about one-fifth of all skin tumors identified in dogs… but this malignancy can also appear in other organs such as the liver, spleen, and digestive tract. Some mast cell tumors behave quietly, with a slow rate of growth and minimal spread or metastasis. Others can become quite aggressive, growing quickly and spreading to other locations in the body. Brachycephalic (flat-faced) breeds of dogs are known to be more prone to this particular type of cancer.

The dark granules that can be seen microscopically actually represent stores of histamine. When the cells of a mast cell tumor are disturbed, they can release the histamine in large amounts, leading to local inflammation and itch or even a systemic anaphylactic-like reaction.

When a mast cell tumor is diagnosed, prompt action is recommended. A variety of tests may be performed to evaluate the overall health of the patient and to try to determine if the tumor is localized or if it has spread to other areas of the body. Determining if a tumor has spread is called staging. This can involve bloodwork, radiographs/ultrasounds, and biopsies.


Most dogs are treated with antihistamine drugs prior to biopsy or removal of a suspected mast cell tumor. This reduces the risk of inflammation and histamine-driven reactions and makes the true margins of the mass more obvious.

Treatment starts with surgical excision of the mass. Once it’s removed, microscopic evaluation can give veterinarians an idea of how aggressively the tumor was behaving (grading), whether or not all of it was removed, and how likely it was to have spread.  

For non-aggressive tumors (low grade/low stage), treatment may be complete with surgical excision. Some patients will require additional surgery, chemotherapy medications, or radiation therapy to address aggressive or metastasized tumors. Many new drug options are now available to help treat dogs with mast cell tumors.

Once a tumor is removed, pet owners are often cautioned that new mast cell tumors can arise in different locations on the skin/body.

For Daisy, surgery was tricky because of the location of the mass on her leg. Her veterinarian had to plan the procedure carefully to make sure all of the mass was removed and that the skin incision could also be closed over the elbow in a manner that did not compromise circulation or put too much tension on the sutures.

Daisy’s mass was sent to a pathologist for microscopic examination. Her skin healed well, and after a tense wait, her family was informed that the tumor was low-grade and appeared to have been removed completely. As a result, no further treatment would be required. However, her family will be watching closely for any new lumps or bumps on her skin.

Claim Outcome

Daisy required $2,249.02 in care for her mast cell tumor. Her Accident and Illness More plan covered $1,799.21** of those fees. We are so happy to know that Pets Plus Us could make it easier for this Miss to get the best treatment for her cancer. We hope she never gets another lump, but if she does, her policy will be there to help her family manage the cost of care.


Learn more about our Accident and Illness plan.
*Name changed for privacy.
**Source: 2023 PTZ Insurance claims data. Value of claims in $ CAD.

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