Mast Cell Tumors

The dreaded diagnosis: mast cell tumor. Mast cell tumors are the most common malignant tumors in dogs, but are rare in cats. Mast cell tumors can be quiet, locally aggressive, or spread like wildfire. They are great imitators, sometimes appearing to be small, benign growths or skin tags. They can look and feel like a lipoma or benign mass under the skin or they can be pink, raised, ulcerated, and swollen. They may grow and shrink, only to enlarge again later. It is impossible to know whether your pet's mass is a mast cell tumor without looking at cells under the microscope.

Healthy normal mast cells form part of the body’s immune system. They can be found in most tissues, but in particular in the skin and the linings of the digestive tract, lungs, mouth and the nose. They are also involved in allergies and allergic reactions. When triggered, the mast cells release large amounts of heparin, histamine, and enzymes.

Mast cell tumors are generally easy to diagnose. A sampling of cells from an impression smear or a fine needle aspirate can be stained and examined under a microscope in your veterinarian's office or sent to a pathology lab for path review. The cells are distinct in appearance, being filled with dark purple granules. Generally, when a mast cell mass is aspirated, the cells will release those granules, resulting in purple spots all over the microscope field. While it is possible to say this IS a mast cell tumor, it is not possible to determine how aggressive the mass will be without a biopsy.


The cause of mast cell tumors is up for debate, just like many cancers. Immune-system suppression or dysfunction and over-vaccination have been implicated by some researchers.

Treatment consists of surgical removal with wide margins. This can be difficult when tumors are located in areas such as limbs where there will not be enough skin to close over areas of wide excision. Biopsy of the mass will determine the grade of the tumor to help predict how the tumor will behave and whether clean margins were realized during surgery. Grade 1 tumors can usually be removed and normally they do not return. Only about 5 to 10% of Grade 2 tumors will return if surgery is done with a wide excision, but about 50% of Grade 3 tumors will return after surgical removal, even with clean margins.

Chemotherapy and radiation may be recommended for higher grade tumors. Unfortunately, there is certainly no guarantee these options will prevent recurrence. Many clients come to my office looking for alternative options to help slow the growth of these masses. While each pet is different, I have a few recommendations that I generally recommend.

  • A clean, commercial human-grade, whole-food diet low in starchy carbs or a home-prepared diet, or a ketogenic diet.
  • Palmitoylethanolamide or PEA, which is a fatty acid amide that supports the healthy function of mast cells and decreases inflammation and granule release.
  • Cannabidiol, which helps block pain and inflammation through cannabinoid receptors. There is some evidence that CBD can have an anti-tumor effect as well.
  • Mushroom supplements for their cancer-fighting aspects. Mushrooms fight cancer in four specific ways: They stimulate the immune system, help immune cells bind to tumor cells, reduce the number of cancer cells (cytotoxic effect), and slow down cancer cell growth. The Japanese government officially recognizes mushroom cancer therapy as a treatment.
  • Omega-3 fatty acids to decrease pain and inflammation. Omega-3's work in conjunction with the endocannabinoid system to decrease spread of cancer throughout the body.
  • IP-6 400 to 800 mg daily - an antioxidant that plays and important role in regulating vital cellular functions, helps reduce tumor size and prevent spread
  • Artemisinin - also known as sweet wormwood, 100 mg twice daily for 11 days on, 3 days off, repeat. Cancer cells take up more iron then normal cells. Artemisinin is attracted to these high iron cells and selectively goes to them. Once inside the cancer cells it reacts with the iron causing free-radical formation which kills the cancer cells.
  • Xue Fu Zhu Yu Tang - Mast cell cancer often arises if there is impaired blood flow to the skin. Without good blood flow the immune system cannot find and destroy the cancer cells that arise. This herb helps promote blood flow to the skin so the immune system can reach the mast cell cancer. In my experience this formula helps to reduce tumor size, occasionally shrink the small tumors completely and prevent formulation of new mast cell tumors. 
  • Golden paste - turmeric has been shown to have cancer-fighting abilities. It is synergistic with the Xue Fu Zhu Yu Tang.

From a traditional veterinary medicine standpoint, these tumors are commonly treated using steroids (prednisone, dexamethasone) and antihistamines (most commonly diphenhydramine). Side effects from long-term use of these drugs make them a poor choice for ongoing management, but they may have short-term benefits that might be worthwhile.

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