Mast Cell Tumors in Dogs

What Are Mast Cells?

Mast Cells are a special type of cell, which are involved in immune function and found primarily in the skin (although they are also found throughout the body). They make up about 20% of the skin cells in a dog, and are responsible for allergy response, among other things. When the body is exposed to particular types of harmful substances, the mast cells release chemical called histamine, which causes the typical allergy-like response. They also produce other vital chemicals which the body needs to survive, called cytokines. Even though mast cells are primarily a type of immune cell, they can become cancerous. Cancer is first and foremost an immune dysfunction disease. Tumors form when the body fails to recognize as invaders the cells that have multiplied improperly.

Mast cell tumors (MCT's) are fairly common tumors in dogs. They are most frequently found in the superficial layers of the skin, on any part of the body. Frequently, there will be ulceration over the area of the tumor, and the dog may scratch or bite at the affected area. The appearance of the tumor does not reveal its potential for spread or recurrence with any certainty. The tumors are usually singular, but dogs may present with multiple nodules, or recurrent ones. Some nodules occasionally enlarge and then regress in size on their own, due to swelling within the tumor itself. This should always raise the suspicion of the presence of an MCT.

Diagnosis of Mast Cell Tumors

Mast cell tumors do not have a specific appearance. However, they are fairly easily detected by a "needle aspirate and cytology." Insertion of a small needle into the tumor (virtually painless) area is followed by examination of the cells under a microscope. Mast cells are large, round cells that usually have dark granules in them. The granules contain substances which, when released, cause swelling, itching, and redness. Infrequently, when a large number of granules discharge their chemical contents into the bloodstream, vomiting, stomach ulcers, shock and even death may result.

MCT Tumor Staging

Mast cell tumors can be somewhat unpredictable in their behavior, relative to other types of tumors in dogs. Because of this, care is taken to "grade" the tumors that are discovered. The grade reflects the degree to which the malignant mast cells differ from normal, non-malignant mast cells. The stage can generally be correlated with tumor behavior, tumor recurrence, and survival of the patient. Mast cell tumors affecting the limbs, head, or neck tend to correlate with a more favorable prognosis than those found on the trunk or groin. Multiple mast cell tumors or those exhibiting rapid growth tend to have a more guarded prognosis. A pathologist determines the tissue grade of the tumor after the tumor is biopsied or removed.

• Grade I: well-differentiated-25% recurrence rate post-surgery
• Grade II: moderately differentiated-44% recurrence rate post-surgery
• Grade III: poorly differentiated-76% recurrence rate post-surgery

How well any dog will respond to therapy is difficult to generalize. Treatment success depends on many factors, such as the dog's age, his or her diet, their medical history, where the tumor is located and how extensive it is and what major systems are involved. Generally speaking, the earlier a mast cell tumor is diagnosed, the better the outcome will be. Since most mast cell tumors occur on or just below the skin, when they are found early, and surgically removed, often the tumor does not recur.

Immune support may be useful to help the dog fighting cancer or other serious health issues.

As Prof. Clements says,

"To me, the answer to cancer lies in the immune system. This is the major reason why I have trouble with Western chemotherapy. Spontaneous remission from cancer only occurs when the patient's immune system acts to clear the cancer. Therefore, stimulation of the patient's immune system to selectively attack the cancer seems to be the key to achieving a successful outcome. New methods in immunotherapy and immunotargeted chemotherapy are likely be the Western methods which lead to the greatest advances in cancer treatment over the next few decades."

(Quote from R.M. Clemmons DVM, PhD
Associate Professor of Neurology & Neurosurgery
Department of Small Animal Clinical Sciences
University of Florida)

Historically, surgery has been the first line treatment for mast cell tumors. This is usually a very good option, depending on where the tumor is located, how extensively it has spread and whether any major organs or underlying structures are involved. After surgery, some type of chemotherapy drug is usually recommended to clean up any remaining cancer cell not removed by the surgery. Chemotherapy and surgery are both effective in removing the bulk of the tumors, but should be seen as only one arm of a multi-pronged approach.

Treatment for Mast Cell Tumors

Treatment for mast cell tumors may involve surgery (the mainstay), chemotherapy, and/or radiation therapy. Recommendations for treatment are based on the type and grade of the tumor, surgical feasibility, and the presence or absence of spread (dissemination) of malignant mast cells throughout the body. Your veterinarian will usually submit blood tests and request abdominal ultrasound or radiographs (x-rays) to determine the likelihood of malignant mast cells elsewhere in the dogs body. Bone marrow biopsies are no longer routinely done, as they have not shown to have high predictive value for tumor staging.

Surgery

For single mast cell tumors, a surgical procedure known as a "wide resection" is performed. This means aggressively excavating the tumor and surrounding tissues so that at least 3 cm of normal tissue in all directions is removed. The margins of the removed tissue are examined by a pathologist to determine the presence of any lingering malignant cells. If negative, we refer to it as "clean margins". If the pathologist suspects the presence of mast cells in the remaining tissues of the surgery site, we refer to it as "dirty margins".

An aggressive surgery early in the course of mast cell tumor disease is associated with the best overall prognosis. A grade I or II tumor that has been completely removed usually requires no other immediate therapy. A grade III tumor, multiple tumors, recurrent tumors, or tumors with dirty margins (those which for anatomical reasons could not be subjected to further surgery) often require follow-up or "adjunct" therapy.

Radiation Therapy

Radiation therapy is an option for dogs whose mast cells tumors are localized, but too large for a clean resection or in an area difficult to resect such as tissues of the facial region, or as follow-up therapy for tumors with dirty margins. Dogs tolerate radiation therapy well, and it can offer long-term control for these tumors. Radiation therapy would not be appropriate for dogs with multiple tumors or those with evidence of disease throughout the body since the radiation beam treats only a single focus of disease.

Chemotherapy

Chemotherapy denotes the administration of certain anti-cancer drugs in order to delay/prevent tumor growth or spread. It may be used before or after surgery, or alone.

K-9 Immunity(TM)

K-9 Immunity(TM) was first developed for Seeing Eye dogs being treated for cancer, and is now available to support dogs fighting serious disease and facing health challenges. K-9 Immunity(TM) has been used in over 10,000 dogs.

K-9 Immunity(TM) contains hetero-polysaccharides, including PSK, PSP and Lentinan. This formula also contains nearly 200 other closely related polysaccharide which trigger other aspects of immune function. These compounds are sometimes referred to as glyconutrients, and are required for correct immune function in all mammals. K-9 Immunity™ is an all-natural, non-toxic daily supplement made from 100% USDA Certified Organic materials. It is made in America at Aloha Medicinals FDA registered facility to the highest pharmaceutical standards.