Medical Oncology: Feline Mast Cell Tumors
What Are Mast Cell Tumors?
Mast cell tumors are comprised of mast cells, immune cells usually involved in allergic reactions. These cells cause the itchy, red bump you get after a mosquito bite or the more severe reactions in people allergic to peanuts or shellfish.
Feline mast cell tumors are categorized as cutaneous (skin), visceral (spleen/liver), or gastrointestinal. Mast cell tumors in these locations can also involve the bone marrow.
Some cats develop only one cutaneous mast cell tumor, and some develop multiple cutaneous tumors. Some cats only develop visceral or intestinal mast cell tumors, and some cats develop tumors in all locations. This is why we recommend all cats diagnosed with a mast cell tumor undergo complete evaluations to determine the extent of their disease before treatment.
What Are The Clinical Signs?
Feline cutaneous mast cell tumors vary in appearance. Many cats have no signs other than the presence of the tumor(s). Some tumors may look like raised white or red bumps within or below the skin’s surface. Others appear as red, ulcerated, bleeding, bruised, and swollen growths. Some tumors appear and remain the same size for months or years, while others show a rapid growth pattern over days or weeks. They can also increase and decrease in size over time. Tumors can be irritating, and cats can scratch, lick, or bite the mass and surrounding skin.
Cats with visceral or intestinal mast cell tumors usually show signs of sickness, such as vomiting, loss of appetite, diarrhea, and lethargy. More severe signs are associated with a more extensive disease burden (e.g., internal spread), but some cats are very sick with only a small amount of disease.
What Diagnostics Are Performed?
Confirmation of the diagnosis is usually done with a needle aspirate of the tumor to collect cells for cytology. Additional diagnostics include sampling of local lymph nodes, abdominal ultrasound (with routine aspirates of the liver and spleen), and potentially bone marrow cytology.
The diagnosis is challenging for tumors located internally (visceral/gastrointestinal). An ultrasound or CT scan may be required to visualize the mass. Other tumors can mimic the appearance of a mast cell tumor with these scans. In many cases, an aspirate with cytology can confirm the diagnosis, but a more invasive procedure (e.g., surgery) may be required.
A concurrent overall health evaluation includes a thorough physical exam (some cats can have multiple skin tumors at the time of diagnosis that can be difficult to see or feel), bloodwork, and urinalysis. Bone marrow sampling is also recommended for most patients.
What Are The Treatment Options?
We recommend surgery for nearly all cutaneous tumors as some may be more aggressive than others, and this cannot be determined by visual appearance. This is true for cats presenting with multiple tumors at the same time or cats who develop more than one mast cell tumor over time. The tumor must be submitted to a pathologist to evaluate (among other things) two critical pieces of information: data regarding the appearance of the cells, which helps determine their potential for spread, and whether the tumor was removed entirely. For some cats, the first surgery does not remove the entire tumor. Options include a second surgery, radiation therapy, or monitoring for regrowth.
When cutaneous mast cell tumors appear in groups, are too large for surgery, or have spread, surgery is insufficient. In those cases, chemotherapy plays a role. There are intravenous (injectable) and oral options (see chart below). Chemotherapy can also be used instead of surgery or radiation therapy to limit the regrowth of an incompletely removed tumor, but the efficacy is unclear.
The prognosis for feline cutaneous mast cell tumors depends on the biopsy features, extent of disease, and ability to achieve adequate local control of tumors. Metastasis, especially beyond a nearby lymph node, indicates a more aggressive clinical course. Monitoring for new masses is essential in such cases, and rapid evaluation is recommended for any cat with a skin mass. Benign tumors are cured with surgery. The prognosis for cats with more aggressive cutaneous mast cell tumors is about one year, on average. This varies depending on the patient.
Surgery is also recommended for cats with visceral or intestinal mast cell tumors. If the disease is too widespread, surgery may not be an option. For those cats, chemotherapy plays a role in treatment. The prognosis for cats with gastrointestinal mast cell tumors is variable but can be 1-2 years with aggressive treatment. For cats with splenic tumors, the prognosis after surgery is an average of about 14 months (compared to 4-6 months without surgery). A subset of cats with both cutaneous mast cell tumors benefit from removing their spleens, meaning their skin lesions resolve with this surgery. Some cats have a more rapid progression of disease and shorter survival.
| Treatment | Indication | Treatment Schedule | Cost |
|---|---|---|---|
| Surgery | Solitary skin tumor, some cases of multiple skin tumors (+/- regional lymph node metastases), splenic tumors, intestinal tumors, others. | Pending further evaluation | $4,500 - $7,000 |
| Radiation Therapy Definitive (post-operative) | Incompletely excised tumors | Daily treatments for 3-4 weeks | $8,000 - $10,000 |
| Radiation Therapy Palliative | Non-resectable tumors | Varies | $1,000 - $5,000 |
| Chemotherapy: Vinblastine (IV) Lomustine (oral) | Higher grade tumors, nonresectable tumors, tumors with metastases | Every one to three weeks | $600 - $700 per treatment |
| Chemotherapy: Tyrosine Kinase Inhibitors (Palladia) | Higher grade tumors, nonresectable tumors, tumors with metastases | Oral chemotherapy given at home every other day or three times per week | $450 - $600 /month (varies with patient weight) |
| Steroids (Prednisolone) | Varies | Oral medication given at home daily | $50 - $300 per month (varies with lab work required) |
Getting Started
Once you have determined the best option, we will work with you to develop an appointment plan. Appointments for patients undergoing treatments and rechecks must be scheduled in advance. All appointments are drop-off appointments.
Drop-offs are between 7:30 am-8:30 am.
Pick-ups occur by 6:00 pm.
No discharges occur between 2:30-3:30 pm as our oncology team is in rounds.
*Costs are estimates. The overall cost depends on patient response. Estimates do not include supportive care or hospitalization.