Friday, September 30, 2011

Cats & Dogs Get Cancer - a look at Mast Cell Tumors

This article is in honor of my niece and her husband’s two boxers, Banks and Sophie, both of whom have recurrent grade I and II mast cell tumors.  And now Banks has another type of mean cancer called epitheliotropic lymphoma.  

This article is about Mast Cell Tumors in dogs (cats get them, too) but also cancer in general.  When people hear the words cancer, and chemotherapy, sometimes their brains shut down.  Cancer is the most common natural cause of death in dogs in the United States and Canada. And while the diagnosis is one that every pet lover dreads, the fact is that cancer is more treatable than ever before. With chemotherapy, I always tell people that for humans, chemotherapy is generally much more potent and has far more side effects than it does for our furry friends.  Oncologists (cancer specialists) for people are trying to cure you so that you see your grandchildren graduate from college, while with pets we are hoping to prolong their life in a reasonable manner, sometimes curing them, and sometimes putting them in remission for quite a while but not until the grandchildren graduate from college!  

I have been there as a pet owner, too.  Just last year both my 14 year old and 4 year old cats developed lymphoma within a month of each other.  The 14 year old was of such a feisty nature, we couldn’t do any form of therapy with her without us all being stressed out, while the 4 year old sailed through diagnostic testing and treatment and went into remission for 4 months (unfortunately he had feline leukemia virus which is why he developed cancer and passed away at such a young age).  He would actually purr and head bump the nurses during chemotherapy visits.  During the entire final four months of his life, he ate well, played with his human, feline, and canine housemates, and was well-loved.  I find that pets often handle their diagnosis, prognosis, and treatment much better than their parents!   I’d like to thank Gina Spadafori and Wendy Brooks, two veterinarians who helped me with this article.

Ways to help keep your pet healthier and less likely to develop cancer:
Make sure your pet has good nutrition, weight-management, and plenty of exercise. A fit dog will have palpable ribs, like running your hand across piano keys, a wasp-like waist and a tucked-in abdomen.  A fit cat will not have a palpable pouch on its belly.  (click here to see Purina's Body Condition Score)

Feed your pet a high-quality diet made by a reputable company (ask your veterinarian what they would recommend) or a home-prepared diet prepared with the help of your veterinarian. Start with the amount of food recommended for your pet and adjust accordingly with how your pet's body responds.  When companies are developing their diets, they feed them to smaller dogs who are usually sexually intact and have a lot of playtime with each other and therefore burn more calories than my couch potato pets, so I don’t feed anywhere near what the bag suggests!  I usually recommend feeding ¾ of what the bag suggests initially, or about 1 cup per 25 lbs of ideal dog body weight per day.  For cats, most cats only need about ½ cup food per day.  Cut down on extra calories for dogs by substituting baby carrots as treats or by adding volume to meals with green beans, frozen, fresh, cooked, or canned.  Some cats will also eat cooked vegetables.  Avoid starchy vegetables due to the calories, and toxic fruits/vegetables such as onions, grapes, and avocados.  Consider adding omega-3 fatty acids (also known as n-3, found in fish oils and other sources) to potentially reduce the risk of developing cancer. 

Add regular exercise, and you and your dog will benefit with greater health and a closer, more vibrant relationship.  Cats can be exercised too!  Toys that they can chase and pounce upon, providing different levels that they can climb on, and tossing their food and making them chase it down to eat it are all methods to encourage some catercise. 

Spay or neuter your pets early in life. Spaying and neutering have been shown to be an effective method of preventing cancer. Spaying has a significant effect of preventing breast cancer if it is done before a dog goes into her first heat cycle. 

Choose clean living for your pets. Eliminate exposure to environmental carcinogens such as pesticides, coal or kerosene heaters, herbicides, passive tobacco smoke, asbestos, radiation and strong electromagnetic fields. Each one of these factors has been suggested to increase the risk of cancer in your pet (and in you). 

Canine Mast Cell Tumors:
Mast cells are meant to participate in the war against parasites, as opposed to the war against bacterial or viral invaders. The mast cell possesses granules of especially inflammatory biochemicals meant for use against invading parasites. (Think of these as small bombs that can be released). When a parasite is near the mast cell, degranulates releasing its toxic biochemical weapons. These chemicals are harmful to the parasite plus serve as signals to other immune cells that a battle is in progress and for them to come and join in.

At least this is what is supposed to happen.  Unfortunately, the mast cell system is also stimulated with other antigens that are of similar shape or size as parasitic antigens. These "next best" antigens are usually pollen proteins and the result is an allergy. Instead of killing an invading parasite, the mast cell biochemicals produce local redness, itch, swelling, and other symptoms we associate with allergic reactions.  As if the mast cell isn't enough of a troublemaker in this regard, the mast cell can form a tumor made of many mast cells. When this happens, the cells of the tumor are unstable. This means they release their toxic granules with simple contact or even at random creating allergic symptoms that do not correlate with exposure to any particular antigen.

Mast cell tumors are especially common in dogs accounting for approximately one skin tumor in every five. The Boxer is at an especially high risk, as are related breeds: English Bulldog, Boston Terrier. Also at higher than average risk are the Shar Pei, Labrador Retriever, Golden Retriever, Schnauzer, and Cocker Spaniel. Most mast cell tumors arise in the skin but technically they can arise anywhere that mast cells are found. The mast cell tumor does not have a characteristic appearance though because of the tumor's ability to cause swelling through the release of granules, it is not unusual for the owner to notice a sudden change in the size of the growth or, for that matter, that the growth is itchy or bothersome to the patient.

Diagnosis can often be made with a needle aspirate, which collects some cells of the tumor with a needle, and the cells are examined under the microscope. The granules have distinct staining characteristics and can be recognized easily. An actual tissue biopsy, however, is needed to grade the tumor; grading is crucial to determining prognosis.

More about grading tumors, prognosis and treatment in upcoming blog!

 By: Dr. Dana Lewis


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